ASoC: msm8952: Fix external speaker gpio logic

The driver parses qcom,msm-spk-ext-pa for both gpio and pinctrl phandle.
That's obviously wrong as it doesn't let us to define both, even though
it's required for the proper external speaker functionality.
Let's expose an additional variable "qcom,cdc-ext-pa-gpios" and use it
for pinctrl phandle.

Change-Id: I1c5fbaeaa575f07c320b3fa8670e51abaffaa0e3