build: don't assume FLASH is the ROM region

Most ARM platforms name their ROM region `FLASH`, but this assumption is
not portable. Have gen_relocate_app refer to ROMABLE_REGION instead of
hard-coding the platform-specific memory region name.

Signed-off-by: Peter Marheine <[email protected]>

Author: tari

scripts/build/gen_relocate_app.py

@@ -55,7 +55,7 @@
 
 LOAD_ADDRESS_LOCATION_FLASH = """
 #ifdef CONFIG_XIP
-GROUP_DATA_LINK_IN({0}, FLASH)
+GROUP_DATA_LINK_IN({0}, ROMABLE_REGION)
 #else
 GROUP_DATA_LINK_IN({0}, {0})
 #endif