checkpatch: deprecate unbounded string functions.

Unbounded string functions are overflow risks.  The 'n'
versions of those functions should be used instead.

Change-Id: Ice0fb3ebdae9aa88cc7e764ffdf68cbed857febf
Signed-off-by: Gregory Bean <gbean@codeaurora.org>
(cherry picked from commit 15e1e97d66dd6a6039c1ec2bd549a632fe361128)
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>