drm/i915/fbc: Nuke bogus single pipe fbc1 restriction

Not sure where the single pipe only restriction came for fbc1.
Nothing I can see that would prevent this.

v2: Nuke no_fbc_on_multiple_pipes() too

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127201222.16669-3-ville.syrjala@linux.intel.com


Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>