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.

Change-Id: I37b13dc870cb797980ffdd978ebf3e15bb624afa
Signed-off-by: David Keitel <dkeitel@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>