drm/amdkfd: Enable SVM on Native mode

This patch enables SVM capability on GFX9.4.3 when
run in Native mode. It also sets best_prefetch and
best_restore locations to CPU as there is no VRAM.

Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>
Acked-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>