drivers: wifi: Fix RPU recovery not being triggered

During watchdog (or any) interrupt processing, RPU accesses are being
made and they assert the wakeup_now flag this causes RPU recovery to not
trigger.

New false or true recovery detection algo:

 Check the time difference b/w last de-assert and assert, and if it
 exceeds minimum time needed for RPU to enter sleep, then not the
 timestamp. This timestamp will be used to compare when a watchdog
 interrupt is received and see if during the last window if host has
 given a chance for RPU to attempt sleep, if yes, then attempt recovery
 else ignore watchdog.

Also, add a Kconfig for the 10s active time that triggers recovery, this
needs to be passed to the FW (once we have enough patch memory).

Also, add a Kconfig for the minimum time needed for RPU to attempt sleep
in positive case.

Also, add a new _ms API for time stamp fetch, this is to avoid
precision loss when converting to and from ms to us and also makes code
readable by avoiding *1000 and /1000.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>