zenfone9: Migrate TARGET board flags from BoardConfig.mk to omni_zenfone9.mk

Inherited makefiles in taro.mk would contain stale or empty value
of TARGET_BOARD_PLATFORM since taro.mk gets scanned earlier than
BoardConfig.mk where TARGET_BOARD_PLATFORM is currently set. In order
to avoid it, migrate TARGET board flags from BoardConfig.mk to taro.mk.

Change-Id: I4644a86248fa3b5a4ff131679f53d9c7807c6398
2 files changed