ASoC: ssm2602: add device tree bindings

Allow the ssm2602/ssm2603/ssm2604 codec driver to be
instantiated from the device tree.

Also, add Kconfig prompts to allow manual selection of both the
I2C and SPI configuration versions of the driver.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>