soc/intel/skylake: Set low maximum temperature threshold for Thermal Device

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: I94d09a28bf1ea07a53cfa04c54752358bafca610
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/22419
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/soc/intel/skylake/chip.h

@@ -527,6 +527,9 @@ struct soc_intel_skylake_config {
 	 * 2 - VR mailbox command sent for IA/GT/SA rails.
 	 */
 	u8 IslVrCmd;
+
+	/* PCH Trip Temperature */
+	u8 pch_trip_temp;
 };
 
 typedef struct soc_intel_skylake_config config_t;