Fix aarch64 build issue with ION

In trying to build ION for aarch64, I came across the following build error:

In file included from /home/jstultz/projects/linux/linaro.android/arch/arm64/include/asm/page.h:39:0,
                 from drivers/staging/android/ion/ion_system_heap.c:17:
/home/jstultz/projects/linux/linaro.android/arch/arm64/include/asm/pgtable-3level-types.h:19:1: error: unknown type name u64
 typedef u64 pteval_t;
 ^
/home/jstultz/projects/linux/linaro.android/arch/arm64/include/asm/pgtable-3level-types.h:20:1: error: unknown type name u64
 typedef u64 pmdval_t;
 ^
...

The problem is asm/page.h doesn't include anything that defines u64, so
add an asm/types.h include to the pgtable-3level-types.h to match upstream
and avoid the issue.

Change-Id: I3f098bf666761ac6b316389a46d37cc449c342d6
Signed-off-by: John Stultz <john.stultz@linaro.org>