ARM: dts: msm8926: Add AB values to the GPU BIMC votes

At least a portion of the GPU's bus usage needs to be taken into
account on low end use cases to prevent underrun for other bus
users.  Add default votes to be taken into account in the BIMC
AB calculation.

Change-Id: I26068027087c0a177a4e0d6a2b15c8859af5c27f
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>