ARM: dts: msm: Add new bus scaling entry for usb2s node

commit f0d6bd14 ("usb: dwc3-msm: Add dynamic pm_qos, clock and bus
voting in host mode") added changes in DWC3 driver to use three bus
scaling votes. With this driver mandates to have three votes in DT node.
Hence add new bus scaling entry for usb device node.

Change-Id: Iac32b7e7f81ce7d7386e59d4b489a37758634e29
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>