phy: sr-usb: Add Stingray USB PHY driver

USB PHY driver supports two types of stingray USB PHYs
 - Type 1 is a combo PHY contains two PHYs, one SS and one HS.
 - Type 2 is a single HS PHY.

These two PHY versons support both Generic xHCI host controller driver
and BDC Broadcom device controller driver.

Signed-off-by: Srinath Mannam <srinath.mannam@broadcom.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>