ARM: dts: omap4-droid4: Configure EHCI so modems can be accessed

Droid 4 has two modems, mdm6600 and w3glte. Both are on the HCI USB
controller.

Let's add a configuration for the HCI so the modems can be enabled.

Note that the modems still need additional GPIO based configuration.

Cc: devicetree@vger.kernel.org
Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Tested-by: Sebastian Reichel <sre@kernel.org>
[tony@atomide.com: left out url]
Signed-off-by: Tony Lindgren <tony@atomide.com>