build: scripts/config - update to kconfig-v5.6

Major changes include:
 - Much more readable reverse dependencies separated in groups
 - Improved recursive dependency report
 - More readable .config files: add comments to signal end of menus
 - More warnings for incorrect Config.in entries, such as a 'choice'
   default not contained in the 'choice'
 - Hability to properly display pseudographics with non-latin locales
 - Recursive dependencies are now treated as errors - this should make
   it harder for them to creep in.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

scripts/config/README

@@ -1,2 +1,24 @@
-These files were taken from the Linux 3.9 Kernel
-Configuration System and modified for the OpenWrt Buildroot.
+These files were taken from the Linux Kernel Configuration System at commit
+089b7d890f972f6b649fedc9259f6b93a18fb970 (Feb 4, 2020) and modified for the
+OpenWrt Buildroot:
+ - removed nconf, gconf, tests and kernel configuration targets
+ - adjusted the Makefile to compile outside the kernel
+ - always use default file when running make all{no,mod,yes}config
+ - added a 'reset' command to reset config when the target changes
+ - allow config reading from & writing to a different file
+ - allow 'source' command to use globs to include multiple files
+ - don't write auto.conf and other files under include/ directory
+ - reverted a commit to allow use of '/' & '.' in unquoted config symbols.
+   There are too many of those in OpenWrt right now.
+ - reverted a commit that was issuing a warning when there were more than
+   one help text.  This is used in a few packages to use different texts
+   for the menuconfig help, and the ipkg package description.
+ - reverted an upstream change that avoids writing symbols that are not
+   visible to .config, which breaks OpenWrt busybox's '.config' generation
+   logic.
+ - use pre-built *.lex.c *.tab.[ch] files by default, to avoid depending on
+   flex & bison.  Rebuild/remove these files only if running make with
+   BUILD_SHIPPED_FILES defined
+
+For a full list of changes, see the repository at:
+https://github.com/cotequeiroz/linux/commits/openwrt/scripts/kconfig