checkpatch: update checkpatch to latest from upstream

Update to commit 6b10df4257367dd0ead49f88df473972c00a8b5c from the Linux
kernel, relevant changes since last update:

 - checkpatch: fix a number of COMPLEX_MACRO false positives
 - checkpatch: improve macros with flow control test
 - checkpatch: warn when casting constants to c90 int or longer types
 - checkpatch: improve the unnecessary initialisers tests
 - checkpatch: improve tests for fixes:, long lines and stack dumps in commit log

Change-Id: Ic4f8d925cd7c076e18eb2f2841913be61239aac2
Signed-off-by: Anas Nashif <anas.nashif@intel.com>