kernel-yocto: allow building from fetcher source dir

kernel-yocto: allow building from fetcher source dir

The linux-yocto recipes themselves always set S="${WORKDIR}/linux" and
arrange for the fetcher default of ${WORKDIR}/git to be renamed before
building.

Part of this rename involves an assumption that the directory used by
the fetcher can be removed as part of the renaming process, or in fact
that renaming is required.

If a derived recipe uses S="${WORKDIR}/git", the checkout phase fails
since the kernel source is removed as part of the processing.

To fix this the code now detects this situation and does not clean the
source directory before renaming the fetcher default (and in fact does
not rename it at all).

(From OE-Core rev: e4ab5efea1a41297f63c96de97270136535b5f0b)

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