ARM: dts: msm: Add extcon phandler with USB node on sdxprairie

USB driver needs to receive vbus/ID(source/sink) notification from
linux pmic driver through policy engine driver. Hence add extcon
phandler with USB node on sdxprairie. Also add qcom,use-pdc-interrupts
flag as DP/DM interrupts are PDC interrupts.

Change-Id: Iaa9a5066ce4c48ed00f57c0106305d97468ed59a
Signed-off-by: Mayank Rana <mrana@codeaurora.org>