ARM: dts: msm: Fix USB3 properties on 8994 Interposer

Add the missing 'qcom,otg-capability' flag to the USB3 device,
as this allows for proper operation with external VBUS detection
provided by the PMIC.

Also, the SSPHY needs to use the L28 regulator instead of S2, and
the discrete VDD voltage levels must be specified.

Change-Id: Id6b76c43ee6d9b7fba5d1ab8066cf845ae46c21c
Signed-off-by: Jack Pham <jackp@codeaurora.org>