dev_ns: gpu (kgsl) power based virtualization.

The approach follows the paradigm described in the "Cells"
paper:
  1. Foreground VPs can suspend the GPU at anytime. Background VPs
     should not stop it from doing so.
  2. Background VPs cannot put the device into suspend mode.
  3. At any point, currently executing processes are not suspended.
     That is, those processes which have taken a reference to the
     device using kgsl_active_count_get method is allowed to complete.
     The dispatch queue is however drained after this so that no more
     incoming requests are taken. This part was already implemented in
     the code.

Signed-off-by: Niket Kandya <niketkandya@gmail.com>