drm/i915: Extract ilk_pch_get_config()

drm/i915: Extract ilk_pch_get_config()

Pull the ilk+ PCH state readout into its own function and relocate
to the appropriate file.

The clock readout parts are perhaps a bit iffy since we depend
on the gmch DPLL readout code. But we can think about the clock
readout big picture later.

Cc: Dave Airlie <airlied@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211015071625.593-6-ville.syrjala@linux.intel.com
Reviewed-by: Dave Airlie <airlied@redhat.com>