util/lint: Exclude devicetree files with custom name from license check

As devicetree files can have different name followed by extension cb
Exclude all .cb file from the license header check.

Change-Id: I37b651eedd77cbf3d3e65ff0f027f971b0a2d2ac
Signed-off-by: Naresh G Solanki <naresh.solanki@intel.com>
Reviewed-on: https://review.coreboot.org/17186
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

util/lint/lint-000-license-headers

@@ -42,7 +42,7 @@ _shipped$|\
 /sdram-.*\.inc$|\
 Makefile\.inc|\
 \.fmd|\
-devicetree.cb|\
+\.cb|\
 \.cfg$|\
 \.spd|\
 config|\