serial: suncore: Add 'ignore_line' argument to sunserial_console_match().

This tells the logic to ignore the line match when deciding whether the
device is the OpenFirmware specified console device or not.

This is going to be used in the SU driver for rsc-console detection.

There is probably a better way to handle this, but this is the least
intrusive solution for now which we can validate won't break any other
cases.

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