util/kconfig: Uprev to Linux 5.13's kconfig

This was originally several commits that had to be squashed into one
because the intermediate states weren't able to build coreboot:

 - one to remove everything that wasn't our own code, leaving only
   regex.[ch], toada.c, description.md and Makefile.inc.
 - one to copy in Linux 5.13's scripts/kconfig and adapt Makefile.inc
   to make the original Makefile work again.
 - adapt abuild to use olddefconfig, simplifying matters.
 - apply patches in util/kconfig/patches.
 - Some more adaptations to the libpayload build system.

The patches are now in util/kconfig/patches/, reverse applying them
should lead to a util/kconfig/ tree that contains exactly the Linux
version + our own 5 files.

Change-Id: Ia0e8fe4e9022b278f34ab113a433ef4d45e5c355
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37152
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

Makefile

@@ -37,7 +37,7 @@ KCONFIG_AUTOADS := $(obj)/cb-config.ads
 KCONFIG_AUTOHEADER := $(obj)/config.h
 KCONFIG_AUTOCONFIG := $(obj)/auto.conf
 KCONFIG_DEPENDENCIES := $(obj)/auto.conf.cmd
-KCONFIG_SPLITCONFIG := $(obj)/config
+KCONFIG_SPLITCONFIG := $(obj)/config/
 KCONFIG_TRISTATE := $(obj)/tristate.conf
 KCONFIG_NEGATIVES := 1
 KCONFIG_STRICT := 1
@@ -196,7 +196,8 @@ real-all: real-target
 .DELETE_ON_ERROR:
 
 $(KCONFIG_AUTOHEADER): $(KCONFIG_CONFIG) $(objutil)/kconfig/conf
-	+$(MAKE) oldconfig
+	$(MAKE) olddefconfig
+	$(MAKE) syncconfig
 
 $(KCONFIG_AUTOCONFIG): $(KCONFIG_AUTOHEADER)
 	true