checkpatch: Add .checkpatch.conf

The checkpatch script doesn't seem to support specifying where to find
the configuration file from, so we need to duplicate the one found in
the main tree.

Signed-off-by: Johan Hedberg <johan.hedberg@silabs.com>

Author: jhedberg

.checkpatch.conf

@@ -0,0 +1,32 @@
+--emacs
+--summary-file
+--show-types
+--max-line-length=100
+--min-conf-desc-length=1
+--typedefsfile=scripts/checkpatch/typedefsfile
+
+--ignore BRACES
+--ignore PRINTK_WITHOUT_KERN_LEVEL
+--ignore SPLIT_STRING
+--ignore VOLATILE
+--ignore CONFIG_EXPERIMENTAL
+--ignore PREFER_KERNEL_TYPES
+--ignore PREFER_SECTION
+--ignore AVOID_EXTERNS
+--ignore NETWORKING_BLOCK_COMMENT_STYLE
+--ignore DATE_TIME
+--ignore MINMAX
+--ignore CONST_STRUCT
+--ignore FILE_PATH_CHANGES
+--ignore SPDX_LICENSE_TAG
+--ignore C99_COMMENT_TOLERANCE
+--ignore REPEATED_WORD
+--ignore UNDOCUMENTED_DT_STRING
+--ignore DT_SPLIT_BINDING_PATCH
+--ignore DT_SCHEMA_BINDING_PATCH
+--ignore TRAILING_SEMICOLON
+--ignore COMPLEX_MACRO
+--ignore MULTISTATEMENT_MACRO_USE_DO_WHILE
+--ignore ENOSYS
+--ignore IS_ENABLED_CONFIG
+--ignore EXPORT_SYMBOL