drm/i915/gen12: Update combo PHY init sequence
The bspec was updated with a minor change to the 'DCC mode select'
setting to be programmed during combo PHY initialization.
v2:
- Keep the opencoded rmw behavior instead of switching to
intel_de_rmw(). We need to read from a _LN register, but write to
the _GRP register to update all lanes.
Bspec: 49291
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230221201836.2886794-1-matthew.d.roper@intel.com