drm/i915/reset: Move pending_fb_pin handling to i915

drm/i915/reset: Move pending_fb_pin handling to i915

Only i915 uses the pending_fb_pin counter to potentially whack
the GPU harder if the display gets nuked during a GPU reset.
Move the atomic counter into the i915 specific bits of code, so
that we don't need to worry about on the display side.

For some reason the overlay code kept the pending_fb_pin counter
elevated for longer than just for the pin, but from now on it'll
just cover the actual pinning part.

Cc: Jouni Högander <jouni.hogander@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260415210411.24750-5-ville.syrjala@linux.intel.com