mb/google/brox: Disable package c state demotion

This needs to be disabled for RPL otherwise we'll hit the assertion:

    [EMERG]  ASSERTION ERROR: file 'src/soc/intel/alderlake/fsp_params.c', line 1066

There is a comment in the referenced file/line in the assertion that
says that "C state demotion must be disabled for Raptorlake J0 and Q0
SKUs."  So, disabling it.

BUG=b:311450057,b:300690448
BRANCH=None
TEST=Tested that we didn't hit this assertion on the device after this
     change

Change-Id: Ib7b2484de2d84c980550fd951f1e30efab0ee197
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79855
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Reviewed-by: Eric Lai <ericllai@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

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

@@ -14,6 +14,10 @@ chip soc/intel/alderlake
 	# S0ix enable
 	register "s0ix_enable" = "1"
 
+	# Disable package C state demotion on Raptorlake as a W/A for S0ix issues
+	# seen on J0 and Q0 SKUs
+	register "disable_package_c_state_demotion" = "1"
+
 	# DPTF enable
 	register "dptf_enable" = "1"