Implement io_uring submission queue entry preparation methods for
epoll_ctl, poll_add and poll_remove.

Poll masks are designated as 32-bit little-endian integers as
specified in liburing's definitions.

Updated io_uring_prep_rw to take in an unsigned 64-bit address instead
of an anytype. io_uring_sqe by default assumes that the address
specified in a submission queue entry is an unsigned 64-bit integer.