powerpc: Ignore the pkey system calls for now

Eliminates warning messages:

<stdin>:1316:2: warning: #warning syscall pkey_mprotect not implemented [-Wcpp]
<stdin>:1319:2: warning: #warning syscall pkey_alloc not implemented [-Wcpp]
<stdin>:1322:2: warning: #warning syscall pkey_free not implemented [-Wcpp]

Hopefully we will remember to revert this commit if we ever implement
them.
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Acked-by: NBalbir Singh <bsingharora@gmail.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/unistd.h

@@ -16,6 +16,10 @@
 
 #define __NR__exit __NR_exit
 
+#define __IGNORE_pkey_mprotect
+#define __IGNORE_pkey_alloc
+#define __IGNORE_pkey_free
+
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>