drm/i915: drop the struct_mutex when wedged or trying to reset

drm/i915: drop the struct_mutex when wedged or trying to reset

We grab the struct_mutex in intel_crtc_page_flip, but if we are wedged
or a reset is in progress we bail early but never seem to actually
release the lock.

Fixes: 7f1847ebf48b ("drm/i915: Simplify checking of GPU reset_counter in display pageflips")
Cc: Chris Wilson <[email protected]>
Signed-off-by: Matthew Auld <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Joonas Lahtinen <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Signed-off-by: Chris Wilson <[email protected]>
Cc: <[email protected]> # v4.7+
(cherry picked from commit ddbb271aea87fc6004d3c8bcdb0710e980c7ec85)
Signed-off-by: Jani Nikula <[email protected]>