drm/amdgpu: add member to store vm fault interrupt masks

This patch adds a member in vmhub structure to store the vm fault interrupt
masks for different version gfxhubs/mmhubs.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>