msm: VPU: Add bus bandwidth scaling support

MSM multimedia IP are supposed to scale the bus according to
their instant bandwidth needs. This change adds this support by
calculating the current VPU load and selecting the right
bandwidth before voting for bus scaling.

Change-Id: I9e1b9698b079b1924881e0c1678fe1467ee83dfa
Signed-off-by: Stephane Viau <sviau@codeaurora.org>