arm/dt: 8974: Set otg_capability flag to get external VBUS notifications

Enable support for otg_capability so that DWC3 can depend on PMIC
for cable connect events in LPM instead of PHY. Also LDOs can be
disabled during suspend so that USB PHY can enter deep power saving
mode.

Change-Id: Icccdd42063eba4fa849b3d9d987ed7dc49287b82
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>