AP_HAL_ChibiOS: add env option to omit hwdef.dat from romfs

libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py

@@ -2574,7 +2574,7 @@ Please run: Tools/scripts/build_bootloaders.py %s
         f = open(hwdat, 'w')
         f.write('\n'.join(self.all_lines))
         f.close()
-        if not self.is_periph_fw():
+        if not self.is_periph_fw() and not os.getenv("NO_ROMFS_HWDEF", False):
             self.romfs["hwdef.dat"] = hwdat
 
     def write_defaulting_define(self, f, name, value):