mm/pkeys: Add an empty arch_pkeys_enabled()

Add an empty arch_pkeys_enabled() in linux/pkeys.h for the
CONFIG_ARCH_HAS_PKEYS=n case.

Split out of a patch by Ram Pai <linuxram@us.ibm.com>.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Reviewed-by: NDave Hansen <dave.hansen@intel.com>

include/linux/pkeys.h

@@ -39,6 +39,11 @@ static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 	return 0;
 }
 
+static inline bool arch_pkeys_enabled(void)
+{
+	return false;
+}
+
 static inline void copy_init_pkru_to_fpregs(void)
 {
 }