powerpc: wire up preadv2 and pwritev2 syscalls

Wire up preadv2/pwritev2 in the same way as preadv/pwritev. Fixes two
build warnings on ppc64.

mpe: Lightly tested with fio (slightly hacked to add the syscall
wrappers):

  fio-4217  [009] ....  1304.635300: sys_preadv2(fd: 3, vec:
  10025821de0, vlen: 1, pos_l: 6253000, pos_h: 0, flags: 1)
  fio-4217  [009] ....  1304.635474: sys_preadv2 -> 0x1000
Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/systbl.h

@@ -384,3 +384,5 @@ SYSCALL(ni_syscall)
 SYSCALL(ni_syscall)
 SYSCALL(mlock2)
 SYSCALL(copy_file_range)
+COMPAT_SYS_SPU(preadv2)
+COMPAT_SYS_SPU(pwritev2)

arch/powerpc/include/asm/unistd.h

@@ -12,7 +12,7 @@
 #include <uapi/asm/unistd.h>
 
 
-#define NR_syscalls		380
+#define NR_syscalls		382
 
 #define __NR__exit __NR_exit
 

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

@@ -390,5 +390,7 @@
 #define __NR_membarrier		365
 #define __NR_mlock2		378
 #define __NR_copy_file_range	379
+#define __NR_preadv2		380
+#define __NR_pwritev2		381
 
 #endif /* _UAPI_ASM_POWERPC_UNISTD_H_ */