drm/amdgpu: add recent pagefault info in vm_manager

Currently page fault information is stored per
vm and which could be freed or stale during
reset. Add it pagefault information in the
vm_manager which is a global space for vm's
and remains valid across.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>