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>
diff --git a/src/southbridge/intel/i82801dx/smihandler.c b/src/southbridge/intel/i82801dx/smihandler.c
index b2b4662..e7a9589 100644
--- a/src/southbridge/intel/i82801dx/smihandler.c
+++ b/src/southbridge/intel/i82801dx/smihandler.c
@@ -276,7 +276,7 @@
 	 * CMOS or even better from GNVS. Right now it's hard
 	 * coded at compile time.
 	 */
-	u8 s5pwr = CONFIG_MAINBOARD_POWER_ON_AFTER_POWER_FAIL;
+	u8 s5pwr = CONFIG_MAINBOARD_POWER_FAILURE_STATE;
 
 	/* First, disable further SMIs */
 	reg8 = inb(pmbase + SMI_EN);