build: allow AutoLoad and AutoProbe to specify modules not included in the package

On out-of-tree modules depending on other out-of-tree modules from a
different tree, module dependencies are not filled properly.
This change helps with adding those dependencies in the AutoLoad call

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43323 3c298f89-4303-0410-b956-a3cf2f4a3e73