wcn36xx: Implement print_reg indication

Some firmware versions sends a "print register indication", handle this
by printing out the content.

Cc: Nicolas Dechesne <ndec@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>