usb: phy: make it a menuconfig

We already have a considerable amount of USB
PHY drivers, making it a menuconfig just
prevents us from adding too much churn to
USB's menuconfig.

While at that, also select USB_OTG_UTILS from
this new menuconfig just to keep backwards
compatibility until we manage to remove
that symbol.

Signed-off-by: Felipe Balbi <balbi@ti.com>