checkpatch: validate SPDX license with spdxcheck.py

checkpatch: validate SPDX license with spdxcheck.py

Use the existing scripts/spdxcheck.py to validate any
SPDX-License-Identifier found in line 1 or 2 of patches or files.

Miscellanea:

o Properly indent the existing SPDX-License-Identifier block.

Link: http://lkml.kernel.org/r/05b832407b24e0a27e419906187cd863bc1617c7.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>