ASoC: rt5640: Add minimal support for RT5642

We have been using rt5640.c codec driver with RT5642 codec chip before commit
022d21f0 ("ASoC: rt5640: add rt5639 support"). That commits starts using
device ID reading in reset register for adding device specific controls and
routes runtime.

Now since device ID appears to be different between RT5640 and RT5642 the
driver doesn't add those controls and routes that are valid also on RT5642.

Fix this by adding a device ID found by debugging and minimal code for
supporting RT5642.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@linaro.org>