ARM: imx: Remove references to platform_bus in mxc code

The bus devices created to be parents for other peripherals
were using platform_bus as a parent, not being platform
devices themselves. Remove the references, making them
virtual devices instead.

Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Acked-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>