drm/amdgpu: For GFX 9.4.3 APU fix vram_usage value

For GFX 9.4.3 APP APU VRAM is allocated in GTT domain. While freeing
memory check for GTT domain instead of VRAM if it is APP APU

Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>