A frequent request have been to be able to provide calibration data from a
file as some of the AP devices store the calibration data on an MTD partition.
This patchset adds support for that and also makes it easier to add Device Tree
support later on.

The calibration data is found by using the id string provided by dev_name()
using this format:

cal-<bus>-<id>.bin

With PCI the id string contains bus, slot and func values. For example for a
PCI device in bus 2 slot 0, ath10k will try to retrieve a calibration data from
a file:

/lib/firmware/ath10k/cal-pci-0000:02:00.0.bin

The calibration data sequence is:

1. Check with request_firmware() if there's a calibration file
   ("cal-<bus>-<id>.bin") on the filesystem for this device. If yes, use that. If
   not, goto 2

2. Check if otp.bin is able to successfully load the calibration data
   from OTP. If yes, use that. If not, goto 3.

4. Print an error message that no calibration data found and stop driver
   initialization for this device.

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