k3: Implement new RIT/XIT function

For the K3 RIT/XIT are now explicitly turned On/Off by calling
rig_get/set_func() and passing RIG_FUNC_R/XIT and the status of 1 or 0.

When setting the RIT/XIT offset by calling rig_set_r/xit, an offset of 0
will clear the RIT/XIT offset but will no longer turn the RIT/XIT
function Off.  Likewise, an offset can be set but not active until the
RIT/XIT function is explicitly turned On.
Update rigctl/d man pages for querying certain parameters

The rigctl and rigctld programs support a so far undocumented feature of
being able to query supported modes in set_mode and set_split_mode,
Funcs in set_func and get_func, Levels in set_level and get_level, Parms
in set_parm and get_parm, as well as the vfo_op, scan, ans set_trn
functions.  The query may be used to get a list of supported tokens for
a given function by a rig backend.