sh: More flexible + SH7780 earlyprintk SCIF support.

This makes the early printk support somewhat more flexible,
moving the port definition to a config option, and making the
port initialization configurable for sh-ipl+g users.

At the same time, this allows us to trivially wire up the
SH7780 SCIF0, so that's thrown in too more or less for free.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>