serial: ifx6x60: expanded info available from platform data

Some platform attributes (e.g. max_hz, use_dma) were being intuited
from the modem type. These things should be specified by the platform
data.

Added max_hz, use_dma to ifx_modem_platform_data definition,
replaced is_6160 w/ modem_type, and changed clients accordingly

Signed-off-by: Russ Gorby <russ.gorby@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>