Add support for Allo Piano DAC 2.1 plus add-on board for Raspberry Pi.

The Piano DAC 2.1 has support for 4 channels with subwoofer.

Signed-off-by: Baswaraj K <jaikumar@cem-solutions.net>
Reviewed-by: Vijay Kumar B. <vijaykumar@zilogic.com>
Reviewed-by: Raashid Muhammed <raashidmuhammed@zilogic.com>