ARM: dts: msm8974pro: Add AB value for the lowest BIMC vote

Bus usage needs to be taken into account on the lowest BIMC vote
to prevent underrun for other bus users. Add default vote to be
taken into account in the BIMC AB calculation.

Change-Id: I73a92116f3e0665495bb085008a8bc34128b1941
Signed-off-by: Patrick Cain <pcain@codeaurora.org>