mb/google/nissa/var/riven: Configure Acoustic noise mitigation

Follow the power team’s recommendation:
- Enable Acoustic noise mitigation
- Set slow slew rate VCCIA and VCCGT to SLEW_FAST_4
- Set FastPkgCRampDisable VCCIA and VCCGT to 1

BUG=b:376165743
TEST=built firmware and verified by power team,
     the acoustic noise can be improved a lot.

Change-Id: Ia71985ef21d634763fc5ae22e4f611f7f5e9652a
Signed-off-by: David Wu <david_wu@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/84908
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <ericllai@google.com>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Jayvik Desai <jayvik@google.com>

src/mainboard/google/brya/variants/riven/overridetree.cb

@@ -24,6 +24,13 @@ fw_config
 end
 
 chip soc/intel/alderlake
+	# Acoustic settings
+	register "acoustic_noise_mitigation" = "1"
+	register "slow_slew_rate[VR_DOMAIN_IA]" = "SLEW_FAST_4"
+	register "slow_slew_rate[VR_DOMAIN_GT]" = "SLEW_FAST_4"
+	register "fast_pkg_c_ramp_disable[VR_DOMAIN_IA]" = "1"
+	register "fast_pkg_c_ramp_disable[VR_DOMAIN_GT]" = "1"
+
 	register "sagv" = "SaGv_Enabled"
 
 	# EMMC Tx CMD Delay