io_uring: use an enumeration for io_uring_register(2) opcodes

/*

 * io_uring_register(2) opcodes and arguments

 */

#define IORING_REGISTER_BUFFERS		0

#define IORING_UNREGISTER_BUFFERS	1

#define IORING_REGISTER_FILES		2

#define IORING_UNREGISTER_FILES		3

#define IORING_REGISTER_EVENTFD		4

#define IORING_UNREGISTER_EVENTFD	5

#define IORING_REGISTER_FILES_UPDATE	6

#define IORING_REGISTER_EVENTFD_ASYNC	7

#define IORING_REGISTER_PROBE		8

#define IORING_REGISTER_PERSONALITY	9

#define IORING_UNREGISTER_PERSONALITY	10

enum {

	IORING_REGISTER_BUFFERS			= 0,

	IORING_UNREGISTER_BUFFERS		= 1,

	IORING_REGISTER_FILES			= 2,

	IORING_UNREGISTER_FILES			= 3,

	IORING_REGISTER_EVENTFD			= 4,

	IORING_UNREGISTER_EVENTFD		= 5,

	IORING_REGISTER_FILES_UPDATE		= 6,

	IORING_REGISTER_EVENTFD_ASYNC		= 7,

	IORING_REGISTER_PROBE			= 8,

	IORING_REGISTER_PERSONALITY		= 9,

	IORING_UNREGISTER_PERSONALITY		= 10,

	/* this goes last */

	IORING_REGISTER_LAST

};

struct io_uring_files_update {

	__u32 offset;