mfd: omap-usb-host: clean up omap_usbhs_init()

We split initializing revision 1 and revision 2 into different
functions. Initialization is now done dynamically so that only
the number of ports available on the system are initialized.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>