nsh_syscmds: update rptun_ping to rpmsg_ping, add cmd_rpmsg.

[wyr8899]

Summary

To support rpmsg ioctl, add cmd_rpmsg function, and update rptun ping to rpmsg ping.
depends on apache/nuttx#11618

Impact

Able to use rpmsg ioctl cmd.

Testing

Tested in sim vela and 86 panel.

[jerpelea]

please add a commit message

[acassis]

@xiaoxiang781216 why rptun and rpmsg commands are implemented as NSH commands? I think it should be just a regular command like "pppd" or other. Also although it is used for test under NSH, keeping it outside will be easier to use as standalone application.

[xiaoxiang781216]

@xiaoxiang781216 why rptun and rpmsg commands are implemented as NSH commands?

Since rptun/rpmsg is a simple mapping to kernel rptun/rpmsg driver, just like cmd_losetup operate on /dev/loop.

I think it should be just a regular command like "pppd" or other.

Yes, it could be move to apps/system, but it belong another task.

Also although it is used for test under NSH, keeping it outside will be easier to use as standalone application.

Since the action of rptun/rpmsg command is very simple:

1. Parse command line argument
2. Open the node under /dev/ and call ioctl

If the user disables nsh, it's simpler to call ioctl directly, instead launch the standalone application.