Add checkpatch.pl config file and Makefile targets

This is used to verify the coding style of patches.

Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>

.checkpatch.conf

@@ -0,0 +1,63 @@
+# Configuration for checkpatch.pl
+# ===============================
+
+# Enable more tests
+--strict
+
+# Quiet
+--quiet
+
+# No per-file summary
+--no-summary
+
+# Don't expect the Linux kernel tree
+--no-tree
+
+# Show file line, not input line
+--showfile
+
+# List of ignored rules
+# ---------------------
+
+# Allow the usage of 'extern' in .c files
+--ignore AVOID_EXTERNS
+
+# There's no BIT macro
+--ignore BIT_MACRO
+
+# Allow CamelCase
+--ignore CAMELCASE
+
+# Comparing to NULL explicitly isn't a bad thing
+--ignore COMPARISON_TO_NULL
+
+# Causes false positives
+--ignore COMPLEX_MACRO
+
+# Don't complain about structs not being const
+--ignore CONST_STRUCT
+
+# Do not check the format of commit messages
+--ignore GIT_COMMIT_ID
+
+# We don't have a MAINTAINERS file, don't complain about it.
+--ignore FILE_PATH_CHANGES
+
+# Writing the continuation on the start of the line can make it clearer
+--ignore LOGICAL_CONTINUATIONS
+
+# Don't complain if a line that contains a string is too long. It's better to
+# have a really long line that can be found with grep.
+--ignore LONG_LINE_STRING
+
+# Allow new typedefs
+--ignore NEW_TYPEDEFS
+
+# Prefer stdint.h types over kernel types
+--ignore PREFER_KERNEL_TYPES
+
+# Parentheses can make the code clearer
+--ignore UNNECESSARY_PARENTHESES
+
+# Don't complain when files are modified in 'include/asm'
+--ignore MODIFIED_INCLUDE_ASM