drm/fourcc: Add Arm 16x16 block modifier

Add the DRM_FORMAT_MOD_ARM_16X16_BLOCK_U_INTERLEAVED modifier to
denote the 16x16 block u-interleaved format used in Arm Utgard and
Midgard GPUs.

Changes from v1:-
1. Reserved the upper four bits (out of the 56 bits assigned to each vendor)
to denote the category of Arm specific modifiers. Currently, we have two
categories ie AFBC and MISC.

Changes from v2:-
1. Preserved Ray's authorship
2. Cleanups/changes suggested by Brian
3. Added r-bs of Brian and Qiang

Signed-off-by: Raymond Smith <raymond.smith@arm.com>
Reviewed-by: Brian Starkey <brian.starkey@arm.com>
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Signed-off-by: Ayan kumar halder <ayan.halder@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004141222.22337-1-ayan.halder@arm.com