checkpatch: change CamelCase test and make it --strict

Do not bleat a message on nominally acceptable CamelCase uses that are
separated by an _ like drm_core_has_MTRR.

CamelCase tests are also a bit noisy against certain types of code
acceptable to some kernel developers.

Make the test applicable only with --strict.

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