1. Fix vizd core caused due to concurrent enqueue and reset of cdbq by taking
cdbq_mutex during enqueue.
2. Reset high and low water marks from shutdown of work queue.

Change-Id: If2e76a31950f6f8a38a64c0438d2bf7206476d78
Merge "1. Fix vizd core caused due to concurrent enqueue and reset of cdbq by taking cdbq_mutex during enqueue. 2. Reset high and low water marks from shutdown of work queue."