mb/google/{rex,ovis}: Decrease EPP to 45% for MTL performance expectation

The default EPP is set at 50%, which is deemed insufficiently
aggressive for meeting the MTL performance expectations in
balance_performance mode.

    # cat /sys/devices/system/cpu/cpu0/cpufreq/energy_performance_preference
    balance_performance
    # iotools rdmsr 0 0x774
    0x0000000080003f06

EPP=45% is giving the required performance in MTL.
    # iotools rdmsr 0 0x774
    0x0000000073003d06

NOTE: Kernel changes are necessary to ensure that the EPP (Energy Performance Preference) configured in the BIOS is not overwritten: https://patchwork.kernel.org/patch/13461932

BUG=b:314275133
TEST=Build and boot.

Change-Id: I1953994cdb4e9363fdd4b4728e3e5236276c06c8
Signed-off-by: Sukumar Ghorai <sukumar.ghorai@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79386
Reviewed-by: Jakub Czapiga <czapiga@google.com>
Reviewed-by: Sumeet R Pawnikar <sumeet.r.pawnikar@intel.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/rex/variants/baseboard/ovis/devicetree.cb

@@ -65,6 +65,10 @@ chip soc/intel/meteorlake
 	register "sagv_freq_mhz[3]" = "6400"
 	register "sagv_gear[3]" = "4"
 
+	# set EPP to 45%: 45 * 256/100 = 115 = 0x73
+	register "enable_energy_perf_pref" = "true"
+	register "energy_perf_pref_value" = "0x73"
+
 	# Set on-board graphics as primary display
 	register "skip_ext_gfx_scan" = "1"
 

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

@@ -62,6 +62,10 @@ chip soc/intel/meteorlake
 	register "sagv_freq_mhz[3]" = "6400"
 	register "sagv_gear[3]" = "4"
 
+	# set EPP to 45%: 45 * 256/100 = 115 = 0x73
+	register "enable_energy_perf_pref" = "true"
+	register "energy_perf_pref_value" = "0x73"
+
 	# Set on-board graphics as primary display
 	register "skip_ext_gfx_scan" = "1"