Allow Chip.global_data as backwards-compatible alias for for Chip.global_data_ecp5.

libtrellis/src/PyTrellis.cpp

diff --git a/libtrellis/src/PyTrellis.cpp b/libtrellis/src/PyTrellis.cpp
index 8133e7e..3ea2f7d 100644
--- a/libtrellis/src/PyTrellis.cpp
+++ b/libtrellis/src/PyTrellis.cpp
@@ -181,6 +181,8 @@
             .def_readwrite("tiles", &Chip::tiles)
             .def_readwrite("usercode", &Chip::usercode)
             .def_readwrite("metadata", &Chip::metadata)
+            // Alias for backwards compatibility.
+            .def_readwrite("global_data", &Chip::global_data_ecp5)
             .def_readwrite("global_data_ecp5", &Chip::global_data_ecp5)
             .def_readwrite("global_data_machxo2", &Chip::global_data_machxo2)
             .def(self - self);