soc/intel/cannonlake: Enable low power S0 Idle capability

This patch sets the ACPI FADT flag ACPI_FADT_LOW_POWER_S0
if S0ix is enabled for the platform. This also sets the
FSPUPD to indicate the status of S0ix on the platform.

TEST= Boot to OS and check the ACPI_FADT_LOW_PWR_IDLE_S0 flag
      is set in FACP table - FADT.Flags[21] bit.

Change-Id: I6214ebb61f25ef8b704e60c8474808493c92e6f6
Signed-off-by: Vaibhav Shankar <vaibhav.shankar@intel.com>
Reviewed-on: https://review.coreboot.org/25292
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/cannonlake/chip.c

@@ -228,6 +228,9 @@ void platform_fsp_silicon_init_params_cb(FSPS_UPD *supd)
 	params->PchHdaAudioLinkSndw3 = config->PchHdaAudioLinkSndw3;
 	params->PchHdaAudioLinkSndw4 = config->PchHdaAudioLinkSndw4;
 
+	/* S0ix */
+	params->PchPmSlpS0Enable = config->s0ix_enable;
+
 	/* USB */
 	for (i = 0; i < ARRAY_SIZE(config->usb2_ports); i++) {
 		params->PortUsb20Enable[i] =