ARM: dts: msm: disable test device for sdxpoorwills

sdxpoorwills doesn't have a separate test SID. The current SID being used
belongs to USB, which is causing issue with usb s1 enablement.
Disable smmu test device.

Change-Id: Id705d3dd0ff295539944719c95e15e16d40fbfee
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>