total of 6 interrupt resources for scc(4) on macio(4). This
is 3 per channel, of which the 1st of each channel is the
interrupt associated with the SCC. The other 2 are for DMA
operation.
Change scc_bfe_attach() to accept an argument that's the
number of interrupts per channel (ipc) and change each bus
front-end (bfe) to pass that argument through a wrapper
for the device_attach method.
For now, we only allocate the 1st interrupt of each channel
to perserve behaviour.
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.
