soc/amd/stoneyridge/Kconfig: Create a power restore option

File soc/amd/stoneyridge/sm.c has a CONFIG_MAINBOARD_POWER_ON_AFTER_POWER_FAIL
that's not used at all and has no control. It's also not used in the
build process. Remove the define from sm.c, create a true Kconfig
definition and use it to define if power should be restored after a power
failure/recovery.

BUG=b:72873003
TEST=Build kahlee. Use serial output to check what is being programmed
to RTC shadow. Build with and without selecting the Kconfig parameter.
Then remove serial output and leave the parameter unselected (always S5
at power recovery).

Change-Id: Iec82cb68cf1e2a820e610f12d8620488662232aa
Signed-off-by: Richard Spiegel <richard.spiegel@silverbackltd.com>
Reviewed-on: https://review.coreboot.org/25002
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
diff --git a/src/soc/amd/stoneyridge/southbridge.c b/src/soc/amd/stoneyridge/southbridge.c
index d2495a6..57bd3f0 100644
--- a/src/soc/amd/stoneyridge/southbridge.c
+++ b/src/soc/amd/stoneyridge/southbridge.c
@@ -557,11 +557,16 @@
 
 void southbridge_final(void *chip_info)
 {
+	uint8_t restored_power = PM_S5_AT_POWER_RECOVERY;
+
 	if (IS_ENABLED(CONFIG_STONEYRIDGE_IMC_FWM)) {
 		agesawrapper_fchecfancontrolservice();
 		if (!IS_ENABLED(CONFIG_ACPI_ENABLE_THERMAL_ZONE))
 			enable_imc_thermal_zone();
 	}
+	if (IS_ENABLED(CONFIG_MAINBOARD_POWER_RESTORE))
+		restored_power = PM_RESTORE_S0_IF_PREV_S0;
+	pm_write8(PM_RTC_SHADOW, restored_power);
 }
 
 /*