drm/radeon/kms: add some loop timeouts in pageflip code

drm/radeon/kms: add some loop timeouts in pageflip code

Avoid infinite loops waiting for surface updates if a GPU
reset happens while waiting for a page flip.

See:
https://bugs.freedesktop.org/show_bug.cgi?id=43191

Signed-off-by: Alex Deucher <[email protected]>
Cc: [email protected]
Reviewed-by: Mario Kleiner <[email protected]>
Tested-by: Simon Farnsworth <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>