Add gpu reset check and exception handling for
page retirement.

v2:
  Clear poison consumption messages cached in fifo after
non mode-1 reset.

Signed-off-by: YiPeng Chai <YiPeng.Chai@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>