kmap_types.h: rename D macro

I tend to use a 'D' debugging macro a lot during debugging.  When I define
it before includes I often get conflicts with kmap_types.h's use of 'D'
too.  It's not very nice when a global include pollutes the name space
like this.

Rename the kmap_types.h D to KMAP_D.  It is only used temporarily in the
header so has no effect on anything else.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>