msm: kgsl: Use bw_vbif governor to vote for GPU msm bus bandwidth

KGSL driver doesn't vote for GPU bus bandwidth by itself, but uses
bw_vbif governor that works with a devbw device representing
corresponding master port.

KGSL driver however votes for ocmem bus bandwith using existing
mechanisms.

Change-Id: I00f763522ee5e314041bb23158dfc37fad242de3
Signed-off-by: Vladimir Razgulin <vrazguli@codeaurora.org>