Backport APIs needed by adau1761 driver.

The following APIs are used by the adau1761 driver, but were not
provided by the Petalinux kernel:

* SOC_DAPM_SINGLE_VIRT()
* snd_soc_dapm_put_volsw_virt()
* snd_soc_dapm_get_volsw_virt()
spi-xilinux-ps: Fix off by one bug.

When determining the baud rate divisor, setting the value to 0b000
results in the ps7 spi bus not working correctly.

The loop to determine the baud rate divisor terminated with the value of
8 which after masking results in a value of 0 being set for the divisori
(which is invalid).  Terminating with a value of 7 allows the divisor to
be set to a valid value.
adau1761-backport: Tweak SPI regmap regbits.

Setting regmap.reg_bits = 24 is not supported in the v3.8 kernel.

Setting to 16 as a hack to get the code to progress farther through the
execution chain.
adau1761-backport: Enable sound/soc/adi directory.

Missed this is previous backport commits.

The files out of sound/soc/adi compile fine, but those in sound/soc/adi
still need some tweaks due to API changes in order to compile.