kgsl_pwrscale: Rework policy sysfs implementation

In the current implementation, the pwrscale policy kobj is
created when the pwrscale driver initializes.  It is then added
to the kobj hierarchy when a governor adds sysfs files.

When a governor removes sysfs files, it frees the kobj.

Then, when a new governor starts up, it attempts to add an
uninitialized kobj.  This fails.

Instead, use a constant kobj for the policy directory,
and add governor-specific attributes under it.  If a
sysfs group is given a name, all attributes in the group
will appear in a subdirectory with that name (see cpufreq
governor tuning variables).  Use this approach for our
governor tuning.

TODO (possibly in a future patch) - Rework this so the
governor attributes can be groups attached directly to
the pwrscale kobj.

Change-Id: I7b8ae6d5e690ee107be037ccaf2e737e52062feb
board-8064-gpu: Increase bus freq at lowest GPU frequency

1000 MBPS is too low for a 1920x1080 panel.  This results in
major UI responsiveness issues when the GPU is at 128 MHz, and
odd behavior from the GPU load measurement algorithm - low load
reported despite awful performance.  At 1500 MBPS bus speed, UI
responsiveness issues at 128 MHz disappear and the GPU will scale
properly when it needs to.

Change-Id: Iea8008d1b106ec4dd172d479d68b99f5d10b3317