ARM: dts: mdm: Add the gpio-usb-detect DT for sdxpoorwills

The non-charger platforms of sdxpoorwills use the gpio-usb-detect
driver for USB detection. Add the device node for it and keep it
disabled.

Change-Id: If5c69e121a50f4f075effbc862685305ef460176
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>