mb/google/poppy/variants/soraka: Set PCH thermal trip point to 75 degreeC

PMC logic shuts down the thermal sensor when CPU is in a C-state and
DTS Temp <= Low Temp Threshold in case Dynamic Thermal Shutdown in
S0ix is enabled.

BUG=b:69110373
BRANCH=none
TEST=Ensure Thermal Device(B0: D20: F2) TSPM offset 0x1c[LTT (8:0)]
value is 0xFA.

Change-Id: I6246300a4376a0194950d4de277af040b10b6c1f
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/22628
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Sumeet R Pawnikar <sumeet.r.pawnikar@intel.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/poppy/variants/soraka/devicetree.cb

@@ -265,6 +265,9 @@ chip soc/intel/skylake
 	# Lock Down
 	register "chipset_lockdown" = "CHIPSET_LOCKDOWN_COREBOOT"
 
+	# PCH Trip Temperature in degree C
+	register "pch_trip_temp" = "75"
+
 	device cpu_cluster 0 on
 		device lapic 0 on end
 	end