Add default UHDM install directory

Signed-off-by: Rafal Kapuscik <rkapuscik@antmicro.com>

systemverilog-plugin/Makefile

diff --git a/systemverilog-plugin/Makefile b/systemverilog-plugin/Makefile
index b984207..9c1e516 100644
--- a/systemverilog-plugin/Makefile
+++ b/systemverilog-plugin/Makefile
@@ -21,6 +21,9 @@
 	  uhdmsurelogastfrontend.cc \
 	  uhdmastreport.cc
 
+# Directory to search for Surelog and UHDM libraries
+UHDM_INSTALL_DIR ?= /usr/local
+
 include ../Makefile_plugin.common
 
 CPPFLAGS += -std=c++17 -Wall -W -Wextra -Werror \