kernel-devsrc: check for localversion files in the kernel source tree

kernel-devsrc: check for localversion files in the kernel source tree

The kernel-devsrc rework doesn't take into account localversion
files in the kernel source tree. This might result in modules with an
incomplete version magic when building out-of-tree using the SDK.

Before:
root@qemux86:~# insmod hello.ko
[   42.000212] hello: version magic '5.0.3-yocto-standard SMP preempt
mod_unload PENTIUMM ' should be '5.0.3-my-custom-release-yocto-standard
SMP preempt mod_unload PENTIUMM '
[   42.008200] hello: version magic '5.0.3-yocto-standard SMP preempt
mod_unload PENTIUMM ' should be '5.0.3-my-custom-release-yocto-standard
SMP preempt mod_unload PENTIUMM '
insmod: can't insert 'hello.ko': invalid module format

After:
root@qemux86:~# insmod hello.ko
[   39.094288] hello: loading out-of-tree module taints kernel.
[   39.108044] Hello World!

Signed-off-by: Beniamin Sandu <beniamin.sandu@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>