ASoC: Introduce SOC_SINGLE_S8_TLV() macro

ASoC: Introduce SOC_SINGLE_S8_TLV() macro

This patch introduces SOC_SINGLE_S8_TLV() macro for volume control
on chips which supports both negative and positive gains with sign
bit on a 8 bit register, Gain ranges from -128 to +127 with a
predefined step size.
Currently we only have support to DOUBLE_S8_TLV() which does not fit
for cases where we just have separate gain control register for each
channel.

One of the Qualcomm SOC msm8916 has such gain control register whose gain
range is from -38.4dB to +38.4dB with step size of 0.3dB.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>