Add SPDX identifier to end of license header in python files

Signed-off-by: Daniel Lim Wee Soong <weesoong.lim@gmail.com>

tests/test_v2x.py

diff --git a/tests/test_v2x.py b/tests/test_v2x.py
index 4e3e47a..d698ae0 100644
--- a/tests/test_v2x.py
+++ b/tests/test_v2x.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 from pathlib import Path
 import os

v2x/__main__.py

diff --git a/v2x/__main__.py b/v2x/__main__.py
index ac39f97..147e81e 100644
--- a/v2x/__main__.py
+++ b/v2x/__main__.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 from . import vlog_to_pbtype
 from . import vlog_to_model

v2x/mux_gen.py

diff --git a/v2x/mux_gen.py b/v2x/mux_gen.py
index a5cebbc..4a0b4e3 100755
--- a/v2x/mux_gen.py
+++ b/v2x/mux_gen.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 """
 Generate MUX.

v2x/vlog_to_model.py

diff --git a/v2x/vlog_to_model.py b/v2x/vlog_to_model.py
index 32fcf22..df13262 100755
--- a/v2x/vlog_to_model.py
+++ b/v2x/vlog_to_model.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 """
 Convert a Verilog simulation model to a VPR `model.xml`

v2x/vlog_to_pbtype.py

diff --git a/v2x/vlog_to_pbtype.py b/v2x/vlog_to_pbtype.py
index 1cb5029..24df3dc 100755
--- a/v2x/vlog_to_pbtype.py
+++ b/v2x/vlog_to_pbtype.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 """\
 Convert a Verilog simulation model to a VPR `pb_type.xml`

v2x/xmlinc/xmlinc.py

diff --git a/v2x/xmlinc/xmlinc.py b/v2x/xmlinc/xmlinc.py
index ac11bbe..b6095a6 100644
--- a/v2x/xmlinc/xmlinc.py
+++ b/v2x/xmlinc/xmlinc.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 import lxml.etree as ET
 import os

v2x/yosys/json.py

diff --git a/v2x/yosys/json.py b/v2x/yosys/json.py
index 344a148..ba4363d 100755
--- a/v2x/yosys/json.py
+++ b/v2x/yosys/json.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 """
 This is intended to provide a range of helper functions around the output of

v2x/yosys/run.py

diff --git a/v2x/yosys/run.py b/v2x/yosys/run.py
index 14d03aa..c5ec023 100755
--- a/v2x/yosys/run.py
+++ b/v2x/yosys/run.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 import json
 import os

v2x/yosys/utils.py

diff --git a/v2x/yosys/utils.py b/v2x/yosys/utils.py
index a4aa31a..2d58c59 100644
--- a/v2x/yosys/utils.py
+++ b/v2x/yosys/utils.py
@@ -5,6 +5,8 @@
 # Use of this source code is governed by a ISC-style
 # license that can be found in the LICENSE file or at
 # https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:	ISC
 
 import re