This change adds support for the ADA4961 BiCMOS RF Digital Gain Amplifier,
(DGA), which is optimized for driving heavy loads out 2.0 GHz and beyond.
The device typically achieves -90 dBc IMD3 performance at 500 MHz and
-85  dBc at 1.5 GHz.

Datasheet link:
 http://www.analog.com/media/en/technical-documentation/data-sheets/ADA4961.pdf

This change re-uses the existing ad8366 driver, as most logic is similar.
Also, this chip has a reset pin which is initialized during probe.
Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>