drm/amdgpu: Check APU supports true APP mode

On GPXIP 9.4.3 APU, in no carveout mode there is no real vram heap and
could be emulated by the driver over the interleaved NUMA system memory
and the APU could also  be in the carveout mode during early development
stage or otherwise for debugging purpose so introduce a new member in
amdgpu_gmc to figure out whether the APU is in the native mode as per
the production configuration. AMD_IS_APU cannot be used for Accelerated
Processing Platform APUs as it might be used in a different context on
previous generations or on small APUs.

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Tested-by: Graham Sider <graham.sider@amd.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>