drm/i915: Extract hsw_configure_cpu_transcoder()

Pull the transcoder specific modeset steps into a single place.
With bigoiner we need to keep in mind wheher we're dealing with
the transcoder or the pipe, and a slightly higher level split makes
that easier.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220124192638.26262-4-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>