sh: add spi header and r2d platform data V3

This patch adds the header file asm/spi.h and board specific code for the
r2d board. The header file contains a structure that should be used to
point out a single spi bus. The board specific code for r2d is updated with
such a structure for the new spi_sh_sci driver. The structure contains a
chip select callback plus information about the R9701 rtc chip which is
attached to the spi bus.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>