iio: amplifiers: ad8366: update device support

Add support for the following digital step attenuators:
- HMC271A: 1dB LSB 5-Bit Digital Attenuator SMT, 0.7 - 3.7 GHz
- ADRF5720: 0.5 dB LSB, 6-Bit, Digital Attenuator, 9 kHz to 40 GHz
- ADRF5730: 0.5 dB LSB, 6-Bit, Digital Attenuator, 100 MHz to 40 GHz
- ADRF5731: 2 dB LSB, 4-Bit, Digital Attenuator, 100 MHz to 40 GHz
- HMC1018A: 1.0 dB LSB GaAs MMIC 5-BIT DIGITAL ATTENUATOR, 0.1 - 30 GHz
- HMC1019A: 0.5 dB LSB GaAs MMIC 5-BIT DIGITAL ATTENUATOR, 0.1 - 30 GHz

Additionally, copyright notice was updated with current year.

Co-developed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Co-developed-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>