build: Allow disabling io_uring

This gives users the chance to reduce the number of dependencies
included, which is generally good practice and also reduces code size.

Furthermore, `io_uring` specifically is a strong contender for something
one may wish to disable due to the syscall API's many security issues[1]

 [1]: https://security.googleblog.com/2023/06/learnings-from-kctf-vrps-42-linux.html

Signed-off-by: Manish Goregaokar <manishsmail@gmail.com>

virtio-devices/Cargo.toml

@@ -14,7 +14,6 @@ block_util = { path = "../block_util" }
 byteorder = "1.4.3"
 epoll = "4.3.3"
 event_monitor = { path = "../event_monitor" }
-io-uring = "0.5.13"
 libc = "0.2.139"
 log = "0.4.17"
 net_gen = { path = "../net_gen" }