drm/i915: Change intel_encoders_<hook>() calling convention

Just pass the atomic state and the crtc to intel_encoders_enable() & co.
Make life simpler when you don't have to think which state (old vs. new)
you have to pass in. Also constify the states while at it.
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191118164430.27265-2-ville.syrjala@linux.intel.com