drm/amdgpu/mes: fix mes ring buffer overflow

wait memory room until enough before writing mes packets
to avoid ring buffer overflow.

v2: squash in sched_hw_submission fix

Fixes: de324625 ("drm/amdgpu: cleanup MES11 command submission")
Fixes: fffe347e ("drm/amdgpu: cleanup MES12 command submission")
Signed-off-by: Jack Xiao <Jack.Xiao@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 34e087e8)
Cc: stable@vger.kernel.org