ARM: dts: add sound device node for 512 skuh flavour

After split of audio node from msm8916-qrd-skuh.dtsi to
msm8916-qrd-skuh.dts sound is not registered for 512 version
of target. Add seperate node for 512 flavour.

Change-Id: If9185a45c948adb3b30b2048e370e4761e7e7c63
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>