drm/amdgpu: cleanup mtype mapping

Unify how we map the UAPI flags to the PTE hardware flags for a mapping.

Only the MTYPE is actually ASIC dependent, all other flags should be
copied over 1 to 1 and ASIC differences are handled later on.

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