drm/msm/gpu: add submit flag to hint which buffers should be dumped

To lower CPU  overhead, future userspace will be switching to pinning
iova and avoiding the use of relocs, and only include cmds table entries
for IB1 level cmdstream (but not IB2 or state-groups).

This leaves the kernel unsure what to dump for rd/hangrd cmdstream
dumping.  So add a MSM_SUBMIT_BO_DUMP flag so userspace can indicate
buffers that contain cmdstream (or are otherwise important to dump).

Signed-off-by: Rob Clark <robdclark@gmail.com>