USB: serial: cp210x: improve baudrate support for CP2102N

CP2102N devices support a lot more baudrates than earlier chips by
SiLabs. These devices are not constrained anymore by the table in AN205,
and are able to generate almost any baudrate in the supported range
with only minimal errors. This has also been verified with a scope on
a physical device. This patch adds support for all baudrates supported
by the CP2102N.

Signed-off-by: Karoly Pados <pados@pados.hu>
[johan: rework on top of an205 and max-speed patches ]
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>