.checkpatch.conf: Set max line length to 96

Linux upstream's checkpatch.pl has a default max line length of 100.
Since coreboot uses 96, add --max-line-length=96 to the config file.

Change-Id: I7737f3d2e0d016b0f0dd82df2865a6b51b667066
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/85435
Reviewed-by: Yidi Lin <yidilin@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

.checkpatch.conf

@@ -1,3 +1,6 @@
+# Override checkpatch's default max line length 100
+--max-line-length=96
+
 # Not Linux, so don't expect a Linux tree.
 --no-tree