mfd: omap-usb-tll: Move configuration code to omap_tll_init()

This is because we want to get rid of platform_data usage from probe().
The only information we need is PORT_MODE, and this can be supplied
to us by the user (i.e. omap-usb-host.c).

We also move channel clock management from runtime PM handlers into
omap_tll_enable/disable().

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>