drm/i915: Nuke the magic FBC_CONTROL save/restore

drm/i915: Nuke the magic FBC_CONTROL save/restore

The FBC_CONTROL save restore is there just to preserve the
compression interval setting. Since commit a68ce21ba0c4
("drm/i915/fbc: Store the fbc1 compression interval in the params")
we've been explicitly setting the interval to a specific
value, so the sace/restore is now entirely pointless.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200908140210.31048-2-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>