ASoC: support ROHM BD28623 codec

This patch adds support of the ROHM BD28623MUV
Class D speaker amplifier for Flat-panel TVs.
This IC delivers an output power of 20W + 20W.

Signed-off-by: Katsuhiro Suzuki <suzuki.katsuhiro@socionext.com>
Signed-off-by: Mark Brown <broonie@kernel.org>