drm/v3d: Define the fourcc modifier for the Broadcom UIF format.

This will be used by Mesa, and potentially other drivers in the
future, to describe tiled buffers.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20180621001703.13522-1-eric@anholt.net


Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>