drm/amdgpu: stop unmapping MQD for kernel queues v3

This looks unnecessary and actually extremely harmful since using kmap()
is not possible while inside the ring reset.

Remove all the extra mapping and unmapping of the MQDs.

v2: also fix debugfs
v3: fix coding style typo

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>