kernel: don't copy .so.dbg files into kernel source install

kernel: don't copy .so.dbg files into kernel source install

In 3.16+ x86-64 kernel builds produce a vdso64.so.dbg file. If this file is
copied into the kernel source install multiple QA failures are triggered.
Specifically, this file triggers a debug package split that results in
files installed but not shipped, and invalid .debug file errors.

By ensuring that .so files are not copied, we avoid this incorrect split
with no impact on future build phases.

(From OE-Core rev: f1f6d153de9dc675b4bf4020799b2365b1b62ec7)

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