Add MIC2 Pre-Amplifier, Mic2 input for Allwinner A10 and Allwinner A20.

Previously, there only the Mic1 input and MIC1 Pre-Amplifier was exposed.
This exposes the Mic2 input and MIC2 Pre-Amplifier.
Signed-off-by: Danny Milosavljevic <dannym@scratchpost.org>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>