drm/i915/reg: add AUD_TCA_DP_2DOT0_CTRL registers

For controlling the audio SDP split.

Bspec: 63837
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/20211001100316.26441-1-jani.nikula@intel.com