ath79: fix 5GHz on QCA9886 variant of ZTE MF286

ath79: fix 5GHz on QCA9886 variant of ZTE MF286

Recently, a strange variant of ZTE MF286 was discovered, having QCA9886
radio instead of QCA9882 - like MF286A, but having MF286 flash layout
and rest of hardware.
To support both variants in one image, bind calibration data at offset
0x5000 both as "calibration" and "pre-calibration" nvmem-cells, so
ath10k can load caldata for both at runtime.

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>