LU-16502 lutf: add headers to lutf C code

LU-16502 lutf: add headers to lutf C code

Add SPDX text and documentation to lutf C code.
This will make it easier for developers to
find where different functionality lives.

Test-Parameters: @lnet
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I67d8acc6b5968e76667130f38018ddcf0fcfd3b0
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53480
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>