zephyr: Detect unsorted config_allowed
zephyr: Detect unsorted config_allowed

When the file is not sorted the check fails, but this is not obvious.
Add an explicit message.

BUG=b:195718112
BRANCH=none
TEST=make buildall -j32

Signed-off-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Change-Id: Ib8b049d985c96567308d6240462a539cbf8b596a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3388358
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