mmc: omap_hsmmc: make it behave well as a module

If we put probe() on __init section, that will never work for multiple
module insertions/removals.

In order to make it work properly, move probe to __devinit section and
use platform_driver_register() instead of platform_driver_probe().

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Venkatraman S <svenkatr@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>