Export the current da flags as bitfield

[imp]

Summary

Export the current flags. They can be useful to other programs wanting to do
special thigns for removable or similar devices.

Convert rotating to a DA flag

Rotating is really a da flag. Convert it to a flag so it will be reported with
the other flags for the device. Deprecate the .rotating sysctl in FreeBSD 14.

Make unmapped I/O a flag as well

Although it's really a flag on the underlying disk, add it to the softc flags as
well since we report the unmapped status as a sysctl. This will let us retire
that as well in the future.

[scottl]

My recommendation is to change the rotating and unmapped sysctls to be SYSCTL_PROC, and have them read the flag. That way you can retire the fields out of the softc now.

[scottl]

Also, this should be MFC'd to 12 and even 11. With that, you can remove in 13 instead of waiting for 14

[imp]

Update, per scottl

Add a sysctl flag to int function. Maybe this should be in kern_sysctl.c