selftests/mm: define types using typedef in pkey-helpers.h

Using #define to define types should be avoided.  Use typedef instead. 
Also ensure that __u* types are actually defined by including
<linux/types.h>.

Link: https://lkml.kernel.org/r/20241209095019.1732120-8-kevin.brodsky@arm.com
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: Keith Lucas <keith.lucas@oracle.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/pkey-helpers.h

@@ -13,13 +13,15 @@
 #include <ucontext.h>
 #include <sys/mman.h>
 
+#include <linux/types.h>
+
 #include "../kselftest.h"
 
 /* Define some kernel-like types */
-#define  u8 __u8
-#define u16 __u16
-#define u32 __u32
-#define u64 __u64
+typedef __u8	u8;
+typedef __u16	u16;
+typedef __u32	u32;
+typedef __u64	u64;
 
 #define PTR_ERR_ENOTSUP ((void *)-ENOTSUP)