mb/google/hatch: Override CPU flex ratio

This patch overrides CPU flex ratio on hatch in order to get
better boot time numbers in vboot_reference.

BUG=b:142264107
TEST=Able to save ~100ms of platform boot time while running with
lower cpu flex ratio (i.e. freq ~1500MHz)

Without this CL

1100:finished vboot kernel verification                802,443 (148,108)

With this CL

1100:finished vboot kernel verification                685,382 (46,496)

Change-Id: Idd1d1c0c04b1f742f17227a1335f27a956ee940d
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36865
Reviewed-by: V Sowmya <v.sowmya@intel.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Pratikkumar V Prajapati <pratikkumar.v.prajapati@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/hatch/variants/baseboard/devicetree.cb

@@ -194,6 +194,9 @@ chip soc/intel/cannonlake
 	register "gpio_pm[COMM_3]" = "0"
 	register "gpio_pm[COMM_4]" = "0"
 
+	# CPU Ratio Override
+	register "cpu_ratio_override" = "15"
+
 	# chipset_lockdown configuration
 	# Use below format to override value in overridetree.cb if required
 	# format: