checkpatch: add --strict tests for braces, comments and casts

Add some more subjective --strict tests.

Add a test for block comments that start with a blank line followed only
by a line with just the comment block initiator.  Prefer a blank line
followed by /* comment...

Add a test for unnecessary spaces after a cast.

Add a test for symmetric uses of braces in if/else blocks.
If one branch needs braces, then all branches should use braces.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>