drm/amdkfd: Add gtt sa related data to kfd_dev struct

This patch adds new fields to kfd_dev struct that are necessary for the new kfd
gtt sa module

Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Alexey Skidanov <Alexey.skidanov@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>