ath10k: add cal_data debugfs file

Provide calibration data used by the firmware to user space via a debugfs file.
This makes it easier to debug calibration related problems.

Example:

sudo cp /sys/kernel/debug/ieee80211/phy0/ath10k/cal_data 1.cal

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>