drm/amdgpu: Determing PTE flags separately for each mapping (v3)

The same BO can be mapped with different PTE flags by different GPUs.
Therefore determine the PTE flags separately for each mapping instead
of storing them in the KFD buffer object.

Add a helper function to determine the PTE flags to be extended with
ASIC and memory-type-specific logic in subsequent commits.

v2: Split Arcturus-specific MTYPE changes into separate commit
v3: Fix return type of get_pte_flags to uint64_t

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