This patch adds a SPI bus on which the SPI devices and drivers register.
This makes it cleaner as SPI devices won't accidently end up probed by
a platform_device driver.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>