util/lint: Exclude util/superiotool from checkpatch

`superiotool` follows its own style (e.g. lot's of missing spaces
and odd placement of braces in the register descriptions).

Change-Id: Ifa33938a0fbac10577cbda10537f856f6f100233
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/28214
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/lint/lint-007-checkpatch

@@ -23,6 +23,7 @@ EXCLUDED_DIRS="^payloads/libpayload/util/kconfig\|\
 ^payloads/libpayload/curses/PDCurses\|\
 ^util/crossgcc/patches\|\
 ^util/kconfig\|\
+^util/superiotool\|\
 ^src/vendorcode\|\
 ^Documentation"