generic syscalls: wire up preadv2 and pwritev2 syscalls

These new syscalls are implemented as generic code, so enable them for
architectures like arm64 which use the generic syscall table.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

include/uapi/asm-generic/unistd.h

@@ -717,9 +717,13 @@ __SYSCALL(__NR_membarrier, sys_membarrier)
 __SYSCALL(__NR_mlock2, sys_mlock2)
 #define __NR_copy_file_range 285
 __SYSCALL(__NR_copy_file_range, sys_copy_file_range)
+#define __NR_preadv2 286
+__SYSCALL(__NR_preadv2, sys_preadv2)
+#define __NR_pwritev2 287
+__SYSCALL(__NR_pwritev2, sys_pwritev2)
 
 #undef __NR_syscalls
-#define __NR_syscalls 286
+#define __NR_syscalls 288
 
 /*
  * All syscalls below here should go away really,