nocturne: configure VR per Intel recommendation

These values are Intel recommended.
IccMax = 28A
DC and AC LL = 4mOhms
Pl2 = 18w

BUG=b:79666828
BRANCH=none
TEST=Enabled p-states with patch 
Change-Id:I82d1516998cc26b789faa5d4e897feb06dc06020 and then
"emerge-nocturne depthcharge coreboot chromeos-bootimage", flash spi
image onto nocturne, boot to kernel and verify device stays alive and
responsive for several minutes without locking up.

Change-Id: I4c67c6a095aecc158e529a6b393baf03ec358a3d
Signed-off-by: Pratik Prajapati <pratikkumar.v.prajapati@intel.com>
Reviewed-on: https://review.coreboot.org/27175
Reviewed-by: Lijian Zhao <lijian.zhao@intel.com>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/google/poppy/variants/nocturne/devicetree.cb b/src/mainboard/google/poppy/variants/nocturne/devicetree.cb
index 32d4f55..235391e 100644
--- a/src/mainboard/google/poppy/variants/nocturne/devicetree.cb
+++ b/src/mainboard/google/poppy/variants/nocturne/devicetree.cb
@@ -62,7 +62,7 @@
 	# Set speed_shift_enable to 1 to enable P-States, and 0 to disable
 	register "speed_shift_enable" = "1"
 	register "dptf_enable" = "1"
-	register "tdp_pl2_override" = "15"
+	register "tdp_pl2_override" = "18"
 	register "psys_pmax" = "45"
 	register "tcc_offset" = "10"
 	register "pch_trip_temp" = "75"
@@ -87,10 +87,10 @@
 	#| Psi4Enable     | 1     | 1     | 1     | 1     |
 	#| ImonSlope      | 0     | 0     | 0     | 0     |
 	#| ImonOffset     | 0     | 0     | 0     | 0     |
-	#| IccMax         | 4A    | 24A   | 24A   | 24A   |
+	#| IccMax         | 4A    | 28A   | 24A   | 24A   |
 	#| VrVoltageLimit | 1.52V | 1.52V | 1.52V | 1.52V |
-	#| AcLoadline     | 14.9  | 5     | 5.7   | 4.57  |
-	#| DcLoadline     | 14.2  | 4.86  | 4.2   | 4.3   |
+	#| AcLoadline     | 14.9  | 4     | 5.7   | 4.57  |
+	#| DcLoadline     | 14.2  | 4     | 4.2   | 4.3   |
 	#+----------------+-------+-------+-------+-------+
 	register "domain_vr_config[VR_SYSTEM_AGENT]" = "{
 		.vr_config_enable = 1,
@@ -116,10 +116,10 @@
 		.psi4enable = 1,
 		.imon_slope = 0x0,
 		.imon_offset = 0x0,
-		.icc_max = VR_CFG_AMP(24),
+		.icc_max = VR_CFG_AMP(28),
 		.voltage_limit = 1520,
-		.ac_loadline = 500,
-		.dc_loadline = 486,
+		.ac_loadline = 400,
+		.dc_loadline = 400,
 	}"
 
 	register "domain_vr_config[VR_GT_UNSLICED]" = "{