drm/i915: Apply the combo PLL frac w/a on DG1

drm/i915: Apply the combo PLL frac w/a on DG1

DG1 apparently needs the combo PLL fractional divider w/a
with 38.4 MHz refclk as well. This isn't listed in bspec, but
looking at the hsd it looks like it was possibly just missed
due to no one having a DG1 around at the time.

This gives us slightly more accurate clocks on DG1.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250401163752.6412-2-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>