msm: kgsl: Add GPU minimum bandwidth vote state

The GPU is usually clock gated when idle i.e NAP state.
Introduce a new state after NAP which lowers the GPU
bandwidth vote to minimum non-zero value so that memory
related components can run at a lower frequency corner,
if possible when GPU is idle.

Change-Id: Iee568e8c3039b35d6b58d7fc0fe72880eee2cace
Signed-off-by: Pranav Patel <pranavp@codeaurora.org>