scripts/update-linux-headers: Handle kernel license no longer being one file

scripts/update-linux-headers: Handle kernel license no longer being one file

The kernel has changed its license documentation, so instead of COPYING
being a stand-alone file that defines the license, it refers to various
other files under LICENSES/. This means we need to copy not just COPYING
but also these other files to our copy of the kernel headers.

Signed-off-by: Peter Maydell <[email protected]>
Message-Id: <20180525132755[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>