msm: kgsl: Allow run time control of bus modification

Add a "bus_split" variable to sysfs.  When it is set to 1 the
bus calculation will run normally.  When set to 0 the default
but vote will be used for each GPU frequency.

Change-Id: I4e4e656664be06669d53fb5765a89943679004f2
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>