drm/i915: Fold i9xx_set_pll_dividers() into i9xx_enable_pll()

Can't think of a good reason why we'd need to program the FP
dividers so early. Let's just do it when programming the rest
of the DPLL.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210715093530.31711-12-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>