LU-6142 libcfs: SPDX for libcfs module

LU-6142 libcfs: SPDX for libcfs module

Convert from verbose license text to SPDX.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ie860bb4d3aaa074f4414b149daa387c118db4003
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57834
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>