ath10k: add firmware crash counters

Add three counters related to firmware crashes or resets.

Usage:

# cat /sys/kernel/debug/ieee80211/phy0/ath10k/fw_reset_stats
fw_crash_counter                2
fw_warm_reset_counter           43
fw_cold_reset_counter           0
#

kvalo: split into it's own patch, add debugfs file and add locking

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>