ASoC: rt5677: Allow arbitrary block read/write via SPI

Added rt5677_spi_read() and refactored rt5677_spi_write() so that
an arbitrary block in the DSP address space can be read/written
via SPI. For example, this allows us to load an ELF DSP firmware
with sparse sections, and stream audio samples from DSP ring buffer.

Signed-off-by: Ben Zhang <benzh@chromium.org>
Acked-by: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>