sh: sh2a scif pdata (sh7201/sh7203/sh7206/mxg)

This patch breaks out the sh2a scif serial port platform
data from a shared platform device to one platform
device per port. Also, add serial ports to the list of
early platform devices.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>