by driver backends to mark individual channels as enabled or not.
The default implementation of this method always mark channels as
enabled.
This method is currently not used, but is added with the PowerQUICC
in mind where the 2nd SCC channel can be disabled.
a different register shift and is fed by a different clock than
we use for UltraSPARC hardware. To deal with this, the regshft and
rclk fields in the class structure are removed and bus frontends
now pass the right regshft and rclk to the probe function where
they're put in the BAS and passed in to subordinate drivers.
controllers typically have multiple channels and support a number
of serial communications protocols. The scc(4) driver is itself
an umbrella driver that delegates the control over each channel
and mode to a subordinate driver (like uart(4)).
The scc(4) driver supports the Siemens SAB 82532 and the Zilog
Z8530 and replaces puc(4) for these devices.
