spi: add support for SuperH SPI

The SH7757 has SPI0 module. This patch supports it.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
[grant.likely@secretlab.ca: fixed Makefile ordering, added
    __dev{init,exit} annotations, removed DRIVER_VERSION (this is
    mainline, the version == the kernel version) and tidied some
    indentation & style stuff]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>