checkpatch: warn on long summary, commit text lines

Warn on summary or commit text lines greater than 75 characters.
The summary and commit text are indented and may wrap on a terminal
if they are longer than 75 characters.

Signed-off-by: Steve Muckle <smuckle@quicinc.com>
(cherry picked from commit e2638df6005402597085a58e01b6dd1cf2bdb8a4)