iio: dac: vf610_dac: Add IIO DAC driver for Vybrid SoC

Add driver support for DAC peripheral on Vybrid SoC.

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>