[SERIAL] sunzilog: Fix instance enumeration.

Just do a linear enumeration so that we handle sun4d systems
correctly.  As a consequence, eliminate the hard coded keyboard and
mouse channel line values, use the CONS_{KEYB,MS} flags instead.

Also, report the keyboard/mouse Zilog channels just like the uart ones
do.

Signed-off-by: David S. Miller <davem@davemloft.net>