[NUCLEO_F746ZG] add exporters files

Author: adustm

workspace_tools/export/gcc_arm_nucleo_f746zg.tmpl

@@ -0,0 +1 @@
+{% extends "gcc_arm_common.tmpl" %}

workspace_tools/export/gccarm.py

@@ -82,6 +82,7 @@ class GccArm(Exporter):
         'NUCLEO_F303K8',
         'NUCLEO_F303RE',
         'NUCLEO_F334R8',
+        'NUCLEO_F746ZG',
         'DISCO_L053C8',
         'NUCLEO_L053R8',
         'NUCLEO_L073RZ',