checkpatch: check for #if 0/#if 1

The #if 0 or #if 1 is used to toggle features. Warn if #if 0 or #if 1
is present and suggest that they can be removed.

[akpm@linux-foundation.org: fix spacing around periods, per Joe\
Link: http://lkml.kernel.org/r/1532625218-24321-1-git-send-email-pheragu@codeaurora.org


Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Signed-off-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>