ALSA: ASoC: Add WM8510 SPI support

Implement SPI support for WM8510, cut'n'pasting from the support for
WM8731 contributed by Cliff Cai and Alan Horstmann since the wire format
is the same for both codecs.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>