dwc3-msm: Add default-bus-vote property to select default USB bus voting

On newer platform USB can operate when system into low power saving mode
like SVS. Currently driver is always voting for NOMINAL bus voting which
would prevent system to go into SVS mode. Hence add default-bus-vote
property to select default bus voting on such platform.

Change-Id: I493a7dd68964fadaada622e68b7b3c62c46ada6b
Signed-off-by: Mayank Rana <mrana@codeaurora.org>