Add helper function to get process device data structure from adev to
update counters.

Update vm faults, page_in, page_out counters will no be executed in
parallel, use WRITE_ONCE to avoid any form of compiler optimizations.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>