ARM: dts: msm: Enable Thermistor Support for msm8909 SKUC

The external thermistor is connected to MPP4. Enable support to read
this through the HKADC by configuring MPP4 to AMUX8 and reading it
through the VADC pre-mux4 channel.

Change-Id: Iab4654d91331f2f75713f3c9f33d1facedbe3828
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>