drm/i915/crt: split out intel_crt_present() to platform specific setup

With new platforms not having CRT support and most conditions in
intel_crt_present() being specific to DDI, split out the CRT
initialization to platform specific blocks in the if ladder. Add new
Pineview block for this.

This puts intel_crt_init() more in line with the rest of the outputs,
and makes it slightly easier for the uninitiated to figure out which
platforms actually have what.

v2: keep gen >= 9 check in intel_ddi_crt_present() (Ville)

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190122082307.4003-1-jani.nikula@intel.com