spi: remove i.MX SPI driver

This driver is in a non working state at the moment and will be replaced
by a bitbang driver which can also handle the newer i.MX variants

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: David Brownell <david-b@pacbell.net>
Acked-by: Andrea Paterniani <a.paterniani@swapp-eng.it>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>