checkpatch: add OpenOCD specific config flags

checkpatch: add OpenOCD specific config flags

This initial setup covers the old commits:
commit 09571d62bc1e ("checkpatch: disable extern and switch indent checks")
commit 2f6f7c442d24 ("checkpatch: remove typedef check")
commit 9ad57e96b3c1 ("checkpatch: remove volatile check")
commit 3da783f62854 ("checkpatch: increase line length to 120")
commit 2af5b97ba31f ("checkpatch: remove __packed and __aligned checks")
commit 164450a01576 ("Change checkpatch.pl tab expanding to 4 characters.")

It also skips the check for SPDX_LICENSE_TAG, not implemented in
OpenOCD yet.
Extend to the check in 'strict' mode and skip all the check that
cannot apply on OpenOCD project.

Change-Id: I6c3bdf27465dc563464fbc8fafbaec696e287624
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/5117
Tested-by: jenkins