kconfig: remove mkconfig and boards.cfg

The old configuration script is no longer necessary.
Nor is boards.cfg a primary database.
We can generate it with the genboardscfg.py tool
based on the latest Kconfig, defconfig and MAINTAINERS.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/.gitignore b/.gitignore
index 5ac2e60..a40c277 100644
--- a/.gitignore
+++ b/.gitignore
@@ -34,6 +34,7 @@
 /SPL
 /System.map
 /u-boot*
+/boards.cfg
 
 #
 # git files that we don't want to ignore even it they are dot-files