powerpc: Wire up io_pgetevents

Wire up io_pgetevents system call on powerpc.

io_pgetevents is a new syscall to read asynchronous I/O events from the
completion queue.

Tested with libaio branch aio-poll[1] and the io_pgetevents test (#22) passed
on both ppc64 LE and BE modes.

[1] https://pagure.io/libaio/branch/aio-poll

CC: Christoph Hellwig <hch@lst.de>
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/systbl.h

@@ -393,3 +393,4 @@ SYSCALL(pkey_alloc)
 SYSCALL(pkey_free)
 SYSCALL(pkey_mprotect)
 SYSCALL(rseq)
+COMPAT_SYS(io_pgetevents)

arch/powerpc/include/asm/unistd.h

@@ -12,7 +12,7 @@
 #include <uapi/asm/unistd.h>
 
 
-#define NR_syscalls		388
+#define NR_syscalls		389
 
 #define __NR__exit __NR_exit
 

arch/powerpc/include/uapi/asm/unistd.h

@@ -399,5 +399,6 @@
 #define __NR_pkey_free		385
 #define __NR_pkey_mprotect	386
 #define __NR_rseq		387
+#define __NR_io_pgetevents	388
 
 #endif /* _UAPI_ASM_POWERPC_UNISTD_H_ */