kernel-yocto: restore kernel-meta data detection for SRC_URI elements

Before the kernel tools were simplified and streamlined, there was code
which not only migrated a patch/cfg/scc to the kernel build tree, it
also migrated any subdirectories of those patches.

The effect of this data migration was that any other meta data in
a patch's directory structure would be available for processing.

While we don't want to do this migration anymore, it is possible to
check the path of any SRC_URI patches, and if they include a "kernel-meta"
subdirectory add it to the search path.

This restores the functionality without the old complexity.

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>