kernel.bbclass: do not mv/link sources when externalsrc enabled
If externalsrc is enabled the 'do_unpack' task is run if the recipe has
some local source files. In the case of kernel recipe this caused the
(externalsrc) source tree to be moved/symlinked. This patch prevents the
behaviour, making sure the source tree is not moved around when
externalsrc is enabled. Instead of moving the source tree,
STAGING_KERNEL_DIR will be a symlink to it.
[YOCTO #6658]
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
