omap_cf oops-in-suspend fix

Convert omap_cf into a platform_driver ... this resolves oopsing during
suspend/resume.

Evidently folk haven't tried suspend/resume on an OSK (the main platform
for this driver) since September or so, which is when platform_device
learned about suspend_late()/resume_early() and stopped being able to
suspend/resume without a having a real platform_driver.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>