ARM: msm: USB_MSM_OTG needs USB_PHY

The Kconfig entry for USB_EHCI_MSM unconditionally selects USB_MSM_OTG,
which is now only visible when USB_PHY is also enabled.

A dependency for this has been added in the USB tree, this adds the
now missing bit in the defconfig.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>