buildman: Support #include files in defconfigs

This is used by some boards in U-Boot and is a convenient way to deal
with common settings where using a Kconfig files is not desirable.

Detect #include files and process them as if they were part of the
original file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: https://source.denx.de/u-boot/custodians/u-boot-dm/-/issues/30
3 files changed