spi: SuperH SPI using SCI

Add support for SPI over SCI pins.  SCI is a very simple serial controller
block that can be found on older SuperH processors.  In theory it is
possible to use the SCI hardware block in syncronous mode, but this version
of the driver simply hooks up the bit banging code on the SCI pins.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
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>