ARM: dts: msm: Add regulator entries for USB device node for msm8939

For USB functionality to work, 1.8v, 3.3v and VDDCX rails
are required for USB PHY. Hence add required regulator entries
for USB device node.

Change-Id: I3be159aaaab3c131f3e3275f601f2f3645b866fd
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>