ASoC: rt5677: fix SPI dependency

The rt5677 codec has gained code that requires SPI to work correctly,
but there is no provision in Kconfig to prevent the driver from
being used when SPI is disabled or a loadable module, resulting
in this build error:

sound/built-in.o: In function `rt5677_spi_write':
:(.text+0xa7ba0): undefined reference to `spi_sync'
sound/built-in.o: In function `rt5677_spi_driver_init':
:(.init.text+0x253c): undefined reference to `spi_register_driver'

ERROR: "spi_sync" [sound/soc/codecs/snd-soc-rt5677-spi.ko] undefined!
ERROR: "spi_register_driver" [sound/soc/codecs/snd-soc-rt5677-spi.ko] undefined!

This makes the SPI portion of the driver depend on the SPI subsystem,
and disables the function that uses SPI for firmware download if SPI
is disabled. The latter may not be the correct solution, but I could
not come up with a better one.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: af48f1d0 ("ASoC: rt5677: Support DSP function for VAD application")
Signed-off-by: Mark Brown <broonie@kernel.org>