checkpatch.conf: ignore imported sbcap *.asn files

Prepare to import files to library/sbcap, which we don't want to be
linted in Ia6743e0a3e7974a5f2dd3ecf74ec331f646f6bc2.

Change-Id: I3ab3253753d32a266bdaf32fb247c2c0139d40d3
diff --git a/.checkpatch.conf b/.checkpatch.conf
new file mode 100644
index 0000000..0882941
--- /dev/null
+++ b/.checkpatch.conf
@@ -0,0 +1 @@
+--exclude ^library/sbcap/.*\.asn$