CRT being the only PCH encoder, we can simplify the crtc enable by
pushing the PCH encoder specific parts to CRT encoder.

v2: add separate hsw_enable_crt (Daniel), rebase
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b117fb524fc571837c83292194fc2ad35e588ec9.1507200657.git.jani.nikula@intel.com