soc/intel/skylake: Add config for mbx command for Intersil VR C-state issues

Config for activating VR mailbox command for Intersil VR C-state issues.
0 - no mailbox command sent.
1 - VR mailbox command sent for IA/GT rails only.
2 - VR mailbox command sent for IA/GT/SA rails.

BUG=b:65499724
BRANCH=none
TEST= build and boot soraka.

Change-Id: Ibcced31b7ba473ffa7368c90c945d07a81a368d4
Signed-off-by: Rizwan Qureshi <rizwan.qureshi@intel.com>
Reviewed-on: https://review.coreboot.org/21680
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/skylake/chip.h

@@ -518,6 +518,14 @@ struct soc_intel_skylake_config {
 		/* coreboot handles locking */
 		CHIPSET_LOCKDOWN_COREBOOT,
 	} chipset_lockdown;
+
+	/*
+	 * Activates VR mailbox command for Intersil VR C-state issues.
+	 * 0 - no mailbox command sent.
+	 * 1 - VR mailbox command sent for IA/GT rails only.
+	 * 2 - VR mailbox command sent for IA/GT/SA rails.
+	 */
+	u8 IslVrCmd;
 };
 
 typedef struct soc_intel_skylake_config config_t;

src/soc/intel/skylake/chip_fsp20.c

@@ -271,6 +271,14 @@ void platform_fsp_silicon_init_params_cb(FSPS_UPD *supd)
 	 */
 	params->SendVrMbxCmd1 = config->SendVrMbxCmd;
 
+	/*
+	 * Activates VR mailbox command for Intersil VR C-state issues.
+	 * 0 - no mailbox command sent.
+	 * 1 - VR mailbox command sent for IA/GT rails only.
+	 * 2 - VR mailbox command sent for IA/GT/SA rails.
+	 */
+	params->IslVrCmd = config->IslVrCmd;
+
 	/* Acoustic Noise Mitigation */
 	params->AcousticNoiseMitigation = config->AcousticNoiseMitigation;
 	params->SlowSlewRateForIa = config->SlowSlewRateForIa;