drm/i915/cnl: extract cnl_set_procmon_ref_values

Move the part that reads the table and sets registers based on the
table to its own function.

v2: Rebase.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170822000356.17330-2-rodrigo.vivi@intel.com