checkpatch: ignore SI unit CamelCase variants like "_uV"

Many existing variable names use SI like variants that should be otherwise
obvious and acceptable.

Whitelist them from the CamelCase message.

Signed-off-by: Joe Perches <joe@perches.com>
Suggested-by: Phil Carmody <phil.carmody@partner.samsung.com>
Acked-by: Phil Carmody <phil.carmody@partner.samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>