mm: cma: make linux/cma.h standalone includible

The header uses types and definitions from the linux/init.h as well as
linux/types.h headers without explicitly including them.  This causes a
failure to compile if they are not implicitly pulled in by includers.

Link: http://lkml.kernel.org/r/20161115133235.13387-1-thierry.reding@gmail.comSigned-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/cma.h

 #ifndef __CMA_H__
 #define __CMA_H__
 
+#include <linux/init.h>
+#include <linux/types.h>
+
 /*
  * There is always at least global CMA area and a few optional
  * areas configured in kernel .config.