[PATCH v3] drm/fourcc: add ARM GPU tile modifier

[Alyssa Rosenzweig]

"AGTB" is jargon-y, but then again, so is "AFBC"... Unless Arm wants to
publish the actual name for the format, this works :)

Thank you for the clarification (in the other emails)

Reviewed-by: Alyssa Rosenzweig <alyssa at rosenzweig.io>