cnss2: Add idle state to bus voting

WLAN driver removes idle bus vote for low throughput traffic
scenarios. Fix it by adding idle state. Remove vote only in
case of system suspend or driver unload.

Change-Id: I504714afc839320ec8099356c9689ea568313470
CRs-Fixed: 2484000
Signed-off-by: Mahesh Kumar Kalikot Veetil <mkalikot@codeaurora.org>