ath10k: provide firmware crash info via debugfs

Store the firmware registers and other relevant data to a firmware crash dump
file and provide it to user-space via debugfs. Should help with figuring out
why the firmware crashed.

kvalo: remove dbglog support, rework and refactor the code to avoid ifdefs and
otherwise simplify it as well

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