msm: kgsl: convert pwrscale to use bus_mod

Use a bus specific speed flag rather than overloading
the least upper bound flag.

Change-Id: I343726e6e0d9885f39c343ed56c1667ab2008aee
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>

Conflicts:
	drivers/devfreq/governor_msm_adreno_tz.c