convert iicsmb to use iicbus_transfer for all operations

[avg]

Summary

Previously the driver used more low level operations like iicbus_start
and iicbus_write. The problem is that those operations are not
implemented by iicbus(4) and the calls were effectively routed to
a driver to which the bus is attached.
But not all of the controllers implement such low level operations
while all of the drivers are expected to have iicbus_transfer.

While there fix incorrect implementation of iicsmb_bwrite and iicsmb_bread.
The former should send a byte count before the actual bytes, while the
latter should first receive the byte count and then receive the bytes.

Test Plan

Only the following commands have been tested:

• quick (r/w)
• send byte
• receive byte
• read byte
• write byte