MAINTAINERS/ACCEL: Add include/drm/drm_accel.h to the accel entry
get_maintainer.pl does not suggest Oded Gabbay, the DRM COMPUTE
ACCELERATORS DRIVERS AND FRAMEWORK maintainer for changes that touch
the Accel Subsystem header - drm_accel.h. This is because that file is
missing from the Accel Subsystem entry. Fix this.