util: Support building a new list of ad-hoc CONFIGs
util: Support building a new list of ad-hoc CONFIGs

Add a separate command for this, so that the file can easily be
regenerated completely.

BUG=b:181323955
BRANCH=none
TEST=./util/kconfig_check.py -c build/blipper/.config
	-a util/config_allowed.txt -p PLATFORM_EC_ -s zephyr/ build
See that the output file is generated

Signed-off-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Change-Id: Ife8e4cee3bcacf3d8206cd598140b88608a13109
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3425450
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec