[ARM] omap: back out 'internal_clock' support

The structures weren't ready for this change:

arch/arm/plat-omap/devices.c:320: error: 'struct omap_mmc_conf' has no member named 'internal_clock'
arch/arm/plat-omap/devices.c:326: error: implicit declaration of function 'omap_ctrl_readl'
arch/arm/plat-omap/devices.c:326: error: 'OMAP2_CONTROL_DEVCONF0' undeclared (first use in this function)
arch/arm/plat-omap/devices.c:328: error: implicit declaration of function 'omap_ctrl_writel'

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>