m2k-dac Trigger re-arm missing from main and release candidate

[gastmaier]

The following change was identified missing from the main and release candidate branch, removing "auto-rearm-trigger"

iio: frequency: m2k-dac: add support for auto trigger rearm

This commit adds support for controlling the HDL auto trigger rearm bit.
The functionality exposed by this bit according to HDL documentation is:
    "Rearm trigger after a DMA buffer push is complete"

Signed-off-by: Dumitru Ceclan <dumitru.ceclan@analog.com>

f5e7574