drivers: nrf_wifi: Add a new stats command that reads from memory

Instead of a command and event mechanism that relies on processors being
active (UMAC/LMAC) add a new command that reads from the RPU memory
directly for all stats, useful in debugging when processors are
crashed/non-functional.

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