Makefile: add support for private-kandou directory
Makefile: add support for private-kandou directory

BUG=b:168930682
BRANCH=none
TEST=make buildall

Signed-off-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Change-Id: I658f309644cdbeb050523cab722de71bb052bf25
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2421301
Reviewed-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>

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