ASoC: rt5645: Add the device tree parser

Modify the RT5645 driver to parse platform data from device tree. This is
missing from previous patch in sound/soc/codecs/rt5645.c, that was present
in v3.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>