OMAP4 Thermal Framework: added PCB temperature sensor

This patch adds kernel driver for PCB temperature sensor
connected on TWL6030 GPADC (Thermistor).
It calls dedicated function to start GPADC conversion and
convert the result into milli-degrees celsius.

Change-Id: I7b573182611bda187f6a38dc01ba65935c8a5c4b
Signed-off-by: Sebastien Sabatier <s-sabatier1@ti.com>
modified for TUNA board by faux123

Conflicts:
	arch/arm/configs/faux_tuna_404_defconfig
	drivers/staging/thermal_framework/sensor/Kconfig
	drivers/staging/thermal_framework/sensor/Makefile