drm/amd/amdkfd: Add GFX12 PTE flag to SVM get PTE function

Add new GFX12 PTE flag AMDGPU_PTE_IS_PTE to svm_range_get_pte_flags
function. This resolves the issues related to SVM enablement in GFX12.

Signed-off-by: Sreekant Somasekharan <sreekant.somasekharan@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>