kernel-yocto: split meta data gathering into patch and config phases

do_kernel_metadata gathers and sanitizes the meta-data that is used
in later steps of the kernel-yocto build process. The processing
takes the form of configuration and patch gathering.

The current single pass of both config and patch gathering means
that patches can't modify in-tree configuration elements (although
this makes tracing configuration changes harder, it is a valid
workflow).

We can divide the routine into a patch and configuration phase, and
call the config variant after patching is done. This keeps the
common parts of the gahering intact, but allows us flexibilty in
when the stages happen.

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