checkpatch: add OpenOCD specific config flags

This initial setup covers the old commits:
commit 09571d62bc ("checkpatch: disable extern and switch indent checks")
commit 2f6f7c442d ("checkpatch: remove typedef check")
commit 9ad57e96b3 ("checkpatch: remove volatile check")
commit 3da783f628 ("checkpatch: increase line length to 120")
commit 2af5b97ba3 ("checkpatch: remove __packed and __aligned checks")
commit 164450a015 ("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

.checkpatch.conf

@@ -1,7 +1,32 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
+--max-line-length=120
+--tab-size=4
+--show-types
+--strict
+
+--ignore AVOID_EXTERNS
+--ignore BLOCK_COMMENT_STYLE
+--ignore CAMELCASE
+--ignore COMPLEX_MACRO
+--ignore CONST_STRUCT
+--ignore ENOSYS
 --ignore FILE_PATH_CHANGES
 --ignore GERRIT_CHANGE_ID
+--ignore LINE_SPACING
+--ignore LOGICAL_CONTINUATIONS
+--ignore MACRO_WITH_FLOW_CONTROL
+--ignore NEW_TYPEDEFS
+--ignore PARENTHESIS_ALIGNMENT
+--ignore PREFER_DEFINED_ATTRIBUTE_MACRO
+--ignore PREFER_FALLTHROUGH
+--ignore PREFER_KERNEL_TYPES
+--ignore SPDX_LICENSE_TAG
+--ignore SPLIT_STRING
+--ignore SSCANF_TO_KSTRTO
+--ignore SWITCH_CASE_INDENT_LEVEL
+--ignore TRACING_LOGGING
+--ignore VOLATILE
 
 # Temporarily lines, to commit checkpatch itself. To be removed!
 --no-tree