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.

CRs-Fixed: 2484000
Change-Id: I245fd7abd0f3ba523b416ae5ff213c84ec9b6def
Signed-off-by: Mahesh Kumar Kalikot Veetil <mkalikot@codeaurora.org>
Signed-off-by: Kai Liu <kaliu@codeaurora.org>