drm/amdgpu: add amdgpu_jpeg_sched_mask debugfs

JPEG_4_0_3 has up to 32 jpeg cores and a single mjpeg video decode
will use all available cores on the hardware. This debugfs entry
helps to disable or enable job submission to a cluster of cores or
one specific core in the ip for debugging. The entry is populated
only if there is at least two or more cores in the jpeg ip.

Signed-off-by: Sathishkumar S <sathishkumar.sundararaju@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>