ARM: dts: msm: Disable usb phy by default on msm8996 vplatform

Disable usb phy by default and only enable them for the targets
which require the support for usb phy.

Change-Id: I55d5cba5ef06d3269cc9600dfec866c0f88b31ab
Signed-off-by: Zhiqiang Tu <ztu@codeaurora.org>