ARM: dts: msm: Add the external micbias for msm8x10 AMIC3

AMIC3 is supported in MSM8610 MTP platform to serve
as the secondary analog mic for stereo recording. Per
HW design, the micbias for AMIC3 is supplied as external
one. Add the configuration to support MSM8610 AMIC3.

Change-Id: Ia25d4b351967bdc86639872bb8117d9e1907791a
Signed-off-by: Kuirong Wang <kuirongw@codeaurora.org>