drm/i915: Clean up PCH_TRANSCONF/TRANS_DP_CTL bit defines

Use REG_BIT & co. for PCH_TRANSCONF/TRANS_DP_CTL bits, and
adjust the naming a some bits to be more consistent.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211112193813.8224-6-ville.syrjala@linux.intel.com


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