phy: tusb1210: implement ->set_mode()

->set_mode() can be used to tell PHY to prepare itself to enter USB
Host/Peripheral mode and that's very important for DRD
configurations.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>