msm: kgsl: Assign dispatch queue based on context priority

Based on context priority, assign a dispatch queue to a context
at context registration time. The dispatch queue id is decided
in a round robin fashion.

Change-Id: I8f9265aa99c22d941397fc204b0a6d8a2b25ec92
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>