drm/i915: Read rawclk_freq earlier

Read the rawclk_freq during runtime info probing, prior to its first use
in computing the CS timestamp frequency. Then store it in the runtime
info, and include it in the debug printouts.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/834
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200216163445.555786-1-chris@chris-wilson.co.uk