drm/i915: Simplify combo PLL frac w/a

drm/i915: Simplify combo PLL frac w/a

We are applying the combo PLL frac w/a to all TGL+ platforms, except
RKL. I *think* all RKL machines use a 24 MHz refclk (certainly all
machines in our CI do) and so technically never need the adjustment.
But let's assume the hardware is exactly the same anyway and simplify
the code by applying the w/a to all TGL+ platforms.

v2: Keep the 38.4 MHz check

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250402171720.9350-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>