wil6210: run-time PM when interface down

Allow run-time suspend when interface is down, keep card alive when
interface is up.
If driver is in wmi only or debug_fw mode run-time PM won't suspend.

Change-Id: Ib6e20979285525b3cc58b0e729fff473039e63c6
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>