drm/amdgpu/gfx11: don't read registers in mqd init

Just use the default values.  There's not need to
get the value from hardware and it could cause problems
if we do that at runtime and gfxoff is active.

Reviewed-by: Mukul Joshi <mukul.joshi@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>