linux-yocto-dev: update to v5.6+

linux-yocto-dev: update to v5.6+

Bumping the revision on linux-yocto-dev to reflect the updated state
of -dev.

The aufs/yaffs2 features are in place, but -rt is not yet available,
so the branches are placeholders for future updates.

This has been tested across all supported architectures and reference
qemu platforms, as well as with closely coupled userspace packages.

We tweak the LICENSE_CHECKSUM as well, since upstream has added an
informational note to the file, but the license is otherwise unchanged.

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