EHCI1 provides an HSIC interface. This interface is exposed on the
board through two pins among the GPIO header.

With the PHY now powered up and responding, enabling the interface when
nothing is connected results in a lot of error messages:

	usb 2-1: device descriptor read/64, error -71
	usb 2-1: device descriptor read/64, error -71
	usb 2-1: new high-speed USB device number 3 using ehci-platform
	usb 2-1: device descriptor read/64, error -71
	usb 2-1: device descriptor read/64, error -71
	usb 2-1: new high-speed USB device number 4 using ehci-platform
	usb 2-1: device not accepting address 4, error -71
	usb 2-1: new high-speed USB device number 5 using ehci-platform
	usb 2-1: device not accepting address 5, error -71
	usb usb2-port1: unable to enumerate USB device

Disable it by default, but leave the entries in the board DTS.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>