drm/vc4: crtc: Add encoder to vc4_crtc_config_pv prototype

vc4_crtc_config_pv() retrieves the encoder again, even though its only
caller, vc4_crtc_atomic_enable(), already did.

Pass the encoder pointer as an argument instead of going through all the
connectors to retrieve it again.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20211025152903.1088803-5-maxime@cerno.tech