ASoC: SigmaDSP: Add regmap support

Add support for loading the SigmaDSP firmware using regmap. This allows us
to transparently use SPI or I2C as the transport protocol on devices which
support them.

For now we keep the old I2C support since we have one user of this which is not
straight forward to convert to regmap, due to variable length registers.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>