checkpatch: recognize only specific tags when ending commit text

There are some very frequently used tags that checkpatch can look
for as an ending to the commit text rather than using a pattern,
which can generate false positives in the "no commit text" rule.

Change-Id: I5b4400017b8273bcd9f5a59b3e28965c0062bef4
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>