UPSTREAM: phy: Add set_mode callback

UPSTREAM: phy: Add set_mode callback

The initial use for this is for PHYs that have a mode related to USB OTG.
There are several SoCs (e.g. TI OMAP and DA8xx) that have a mode setting
in the USB PHY to override OTG VBUS and ID signals.

Of course, the enum can be expaned in the future to include modes for
other types of PHYs as well.

Change-Id: Iebc730d7e41c2910fa1be98cbf275d2c73358050
Suggested-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Huang, Tao <huangtao@rock-chips.com>
(cherry picked from commit 300eb0139cf27044c67f6005ff17b8434c7843f0)