usb: phy: Add set_params function

Add a function interface to allow USB controllers to call on PHY
to do specific parameter settings not performed as part of the
init call. For example, this could be used to set or reset tuning
parameters during the course of normal operation.

Change-Id: I3612fcd129a7612b4b60d62d7538b34867c72c2d
Signed-off-by: Jack Pham <jackp@codeaurora.org>