phy: phy-brcm-usb-init: Power down USB 3.0 PHY when XHCI disabled

Set PHY3_IDDQ_OVERRIDE in the xhci uninit routine. This will save
additional power when the XHCI driver is not enabled.

Fixes: 49859e55 ("phy: usb: phy-brcm-usb: Add Broadcom STB USB phy driver")
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>