* bootloader_message.cpp is the only file using
BOOTLOADER_MESSAGE_OFFSET_IN_MISC and WIPE_PACKAGE_OFFSET_IN_MISC,
so we can move their definitions to the cpp.
This prevents the need to set BOARD_RECOVERY_BLDRMSG_OFFSET
in every module that includes the header.
* Global cflags are no longer supported Oreo and up,
so set the BOARD_RECOVERY_BLDRMSG_OFFSET via make variable
* Simplify logic, always set BOARD_RECOVERY_BLDRMSG_OFFSET.
Change-Id: I2b902bcce7f5ca13472e0ac30ac01b4991294dbe
