drm/i915: Change .crtc_enable/disable() calling convention

Just pass the atomic state+crtc to the .crtc_enable()
.crtc_disable(). Life is easier when you don't have to think
whether to pass the old or the new crtc state.

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/20191118164430.27265-11-ville.syrjala@linux.intel.com