checkpatch: verify SPDX comment style

checkpatch: verify SPDX comment style

Using SPDX commenting style // or /* is specified for various file types
in Documentation/process/license-rules.rst so add an appropriate test for
.[chsS] files because many proposed file additions and patches do not use
the correct style.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Joe Perches <[email protected]>
Cc: Rob Herring <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>