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>

Documentation/getting_started/kconfig.md

@@ -55,10 +55,6 @@ command line.
 - savedefconfig - Creates a ‘defconfig’ file, stripping out all of the symbols
   that were left as default values.  This is very useful for debugging, and is
   how config files should be saved.
-- silentoldconfig - This evaluates the .config file the same way that the
-  oldconfig target does, but does not print out each question as it is
-  evaluated.  It still stops to query the user if an option with no answer in
-  the .config file is found.
 
 
 ### Targets not typically used in coreboot