All DRM formats are defined in terms of little-endian words, so RGB formats
like XRGB actually have the elements in the opposite order order in memory
to the order they are in the name.

This does not affect YUYV and similar YUV 4:2:2 formats, which are in the
expected order.

DRM_FORMAT_R8 was added in libdrm 2.4.68.
DRM_FORMAT_R16 was added in libdrm 2.4.82.

Signed-off-by: Jun Zhao <jun.zhao@intel.com>
Signed-off-by: Mark Thompson <sw@jkqxz.net>

Found-by: James Almer <jamrial@gmail.com>