devfreq: Weight stall cycles more for GPU bus DCVS

Update GPU Bus DCVS to weight high stall cycles (as a percentage
of total bus usage) heavier in order to vote up the bus when the
GPU is stalling a lot waiting for data.

Change-Id: I8a331a48a1ab737c51f1001ea1991f09af9ef900
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>