ARM: dts: msm: Enable Thermistor Support for msm8905 QRD SKUB

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

Change-Id: I47e53164de484b67ea0d75ad50a195257ecdcd0b
Signed-off-by: Asha Magadi Venkateshamurthy <amagad@codeaurora.org>