Fill port_clock and hw.adjusted_mode.crtc_clock with the actual
frequency we're going to be getting from the hardware. This will
let us accurately compute all derived state that depends on those.

v2: Reintroduce iCLKIP WARN
v3: Try to deal with VLV/BXT DSI PLL as well

Reviewed-by: Jani Nikula <jani.nikula@intel.com> #v1
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220907091057.11572-8-ville.syrjala@linux.intel.com