wil6210: system power management

Support for the system suspend/resume.
In preparation for the run-time PM, implementation made
run-time PM friendly: common for system and run-time PM
code factored out as generic functions, albeit is_runtime
parameter value is always false currently.

For debug purposes, "PM" debug category introduced.

Policy: AP-like interface can't be suspended; otherwise
suspend is allowed. Hardware brought down if interface
was up. Connection, if existed, get lost.
Interface will be brought up upon resume if it was up
before suspend.

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>