wlcore: Use generic runtime pm calls for wowlan elp configuration

With runtime PM enabled, we can now use calls to pm_runtime_force_suspend
and pm_runtime_force_resume for enabling elp during suspend when wowlan
is enabled and waking the chip from elp on resume.

Remove the custom API that was used to ensure that the command
that is used to allow ELP during suspend is completed before the system
suspend.

Signed-off-by: Eyal Reizer <eyalr@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>