yas529 magnetometer

[xc-racer99]

Branch created at https://github.com/PabloPL/linux/tree/for-upstream/yas529-iio and is heavily inspired by the invesense driver (eg https://android.googlesource.com/kernel/tegra/+/f1e961e877025f60cc409180350a3def85f26f64/drivers/misc/inv_mpu/compass/yas529-kernel.c) as opposed to our stock one.

Appears to work as expected, although the calibration and/or scale of it may be off (magnetic sensors are way outside my knowledge range)

Info sheet at https://www.digchip.com/datasheets/parts/datasheet/535/YAS529-pdf.php but there's no public datasheet.