checkpatch: don't emit the CamelCase warning for PageFoo

I'm getting a ton of these:

  WARNING: Avoid CamelCase: <PageTransHuge>
  #140: FILE: mm/migrate.c:1576:
  +       if (PageTransHuge(page) && page_count(page) != 3) {

So exclude anything which starts with "Page".

Tested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>