feat(mediatek): support coreboot BL31 loading

The ChromeOS project uses Coreboot as BL2 instead of MediaTek regular
bootloader, so we use COREBOOT flag to support Coreboot boot flow.

Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Change-Id: I45e95ea51e90158187452eba52fc58090d1c60a4
3 files changed