sm501: add uart support

This patch extends the sm501 mfd with 8250 uart support. We're currently
doing this in the board specific r2d-1 code already, but it would be nice to
do move things into the mfd since it's more chip specific than board specific.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>