drm/i915: Move stuff into intel_dpll_crtc_compute_clock()

drm/i915: Move stuff into intel_dpll_crtc_compute_clock()

Move some checks into intel_dpll_crtc_compute_clock() from the
caller. Avoids the caller from having to worry about all this
crap.

We'll also reorder the hw.enable vs. shared_dpll checks since
it makes sense to sanity check that we've cleared out the
old shared_dpll even if the pipe is getting disabled.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220325123205.22140-6-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>