ASoC: wcd-spi: add SPI bus arbitration logic

On some platforms, WCD SPI bus can be shared with other processors
(ex: sensor processor). In such cases, there is need for software
to arbitrate the bus control. Add functionality to perform SPI bus
arbitration.

Change-Id: I7df933f55ac5035a55173a04e74b74f7af1f7ece
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>