devtools: make checkpatch cleaner for renamed files

devtools: make checkpatch cleaner for renamed files

When a file is renamed, a normal diff will include all the code of
the renamed file, and checkpatch will find warnings and errors,
even though it's just a rename.

This change will result in a 'rename' line in the diff, resulting
in a much cleaner checkpatches result.

Signed-off-by: David Hunt <david.hunt@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>