Kconfig: Unify power-after-failure options

The newest and most useful incarnation was hiding in soc/intel/common/.
We move it into the Mainboard menu and extend it with various flags to
be selected to control the default and which options are visible. Also
add a new `int` config MAINBOARD_POWER_FAILURE_STATE that moves the
boolean to int conversion into Kconfig:
  0 - S5
  1 - S0
  2 - previous state

This patch focuses on the Kconfig code. The C code could be unified as
well, e.g. starting with a common enum and safe wrapper around the
get_option() call.

TEST=Did what-jenkins-does with and without this commit and compared
     binaries. Nothing changed for the default configurations.

Change-Id: I61259f864c8a8cfc7099cc2699059f972fa056c0
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/29680
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/southbridge/intel/ibexpeak/lpc.c

@@ -174,7 +174,7 @@ static void pch_power_options(struct device *dev)
 	/* Get the chip configuration */
 	config_t *config = dev->chip_info;
 
-	int pwr_on=CONFIG_MAINBOARD_POWER_ON_AFTER_POWER_FAIL;
+	int pwr_on = CONFIG_MAINBOARD_POWER_FAILURE_STATE;
 	int nmi_option;
 
 	/* Which state do we want to goto after g3 (power restored)?