Add util/u_drm_fourcc.h; Add PREFERRED_DRM_MODIFIER env-var for Intel drivers
util/u_drm_fourcc.h
(and related py/c code) provides some utility functions for drm_fourcc.h
.
PREFERRED_DRM_MODIFIER
is an environment variable that raises the priority of the specified modifier. It doesn't guarantee this modifier will be used because modifier support depends on the platform.