ARM: S3C2412: SoC has the fractional baud rate register

The S3C2412 has a fractional baud rate register, this patch adds the
corresponding flag to the UART definition to allow generation of more
precise baud rates for the various clock combinations.

Signed-off-by: Michel Pollet <buserror@gmail.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>