USB: ehci-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.

This adds an appropriate dependency and enables USB_PHY in the msm
defconfig, avoiding the Kbuild warning:

warning: (USB_EHCI_MSM) selects USB_MSM_OTG which has unmet direct dependencies (USB_SUPPORT && USB_PHY && (USB || USB_GADGET) && ARCH_MSM)

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>