Add support for MT7622 reference board

This adds a general board file based on MT7622 SoCs from MediaTek.
This commit is adding the basic boot support for the MT7622 rfb.

Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Reviewed-by: Ryder Lee <ryder.lee@mediatek.com>
Tested-by: Frank Wunderlich <frank-w@public-files.de>
8 files changed