msm: kgsl: Add support for the A540 GPU

Add support for the A540 GPU device:
   * Add entry to the GPU list and add adreno_is_a540() functions
   * Add VBIF settings
   * Add hardware clock gating values

Change-Id: Ibd653597400ded01ca05607fbbdafea3e86e177f
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>
Signed-off-by: Oleg Perelet <operelet@codeaurora.org>