nvme: move submit_io to src/io-cmds

[ikegami-t]

This is to move other IO commands as same.

[igaw]

Good idea! The nvme.c files is way to big, so splitting into smaller pieces is a good thing to do.

[28](https://github.com/linux-nvme/nvme-cli/actions/runs/31263410067/job/93117592364?pr=3791#step:5:229)
../src/io-cmds.c: In function 'submit_io':
../src/io-cmds.c:190:49: error: implicit declaration of function 'basename' [-Wimplicit-function-declaration]
  190 |                                                 basename(argv[optind]));
      |                                                 ^~~~~~~~

There is shr_basename which should fix this problem.

[igaw]

One thing we need to figure out is how to split up the plugin registry. Currently, it needs to be in nvme.c which makes it a bit ugly. That's also why main is in nvme.c.

[ikegami-t]

Just fixed the warning by including libgen.h instead of using shr_basename. If needed I will do change basename to shr_basenem by additional patch since currently basename used by other implementation also.
About the nvme.c yes I tried to change the static command entry function to global but seems not easy to do. So for now I am thinking to split the IO commands as same fabrics commands as only the static command entry functions are still remained in nvme.c. We may split the IO commands as same with the plugins commands but not sure.
Thank you.