ath10k: introduce a stricter scan state machine

This aims at fixing some rare scan bugs related to
firmware reporting unexpected scan event
sequences.

One such bug was if spectral scan phyerr reporting
prevented firmware from properly propagating scan
events to host. This led to scan timeout. After
that next scan would trigger scan completed event
first (before scan started event) leading to
ar->scan.in_progress and timeout timer states to
be overwritten incorrectly and making the very
next scan to hang forever.

Reported-by: Janusz Dziedzic <janusz.dziedzic@tieto.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>