devfreq: Use busy cycles only for GPU bandwidth decisions

Remove using the waiting bandwidth cycles for deciding
when to change bandwidth levels.

Change-Id: I65341c5c115684f19b5a3b2522d362e80315f2c9
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>