drm/i915/dsi: Split icl+ D-PHY vs. DSI timing steps

The programming of the DPHY vs. DSI _TIMING registers are
two separate steps in the TGL+ bspec sequence, with some
other stuff in between. Implement the same split.
Windows also seems follow the bspec TGL+ sequence, even
on ICL/JSL.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230608203057.23759-5-ville.syrjala@linux.intel.com