drm/i915/hdmi: Introduce intel_hdmi_tmds_clock()

Rename intel_hdmi_port_clock() into intel_hdmi_tmds_clock(), and
move the 4:2:0 TMDS clock halving into intel_hdmi_tmds_clock() so
the callers don't have to worry about such details.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211015133921.4609-4-ville.syrjala@linux.intel.com


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