Makefile: Add a target to create the .cfg files

A common requirement when converting CONFIG options to Kconfig is to check
that the effective configuration has not changed due to the conversion. Add
a target which creates this configuration (in the form of u-boot.cfg) but
does not build U-Boot. This speeds up the checking.

Signed-off-by: Simon Glass <sjg@chromium.org>
1 file changed