To avoid compilation breakage on platform that doesn't
support DM PHY but uses xhci-dwc3 driver, add the missing
CONFIG_PHY flag.
Introduced by patch :
84e53877 "usb: host: xhci-dwc3: Add generic PHY support"
Cc: Ran Wang <ran.wang_1@nxp.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reported-by: Ran Wang <ran.wang_1@nxp.com>