staging: OMAP4+: thermal: introduce bandgap temperature sensor

In the System Control Module, OMAP supplies a voltage reference
and a temperature sensor feature that are gathered in the band
gap voltage and temperature sensor (VBGAPTS) module. The band
gap provides current and voltage reference for its internal
circuits and other analog IP blocks. The analog-to-digital
converter (ADC) produces an output value that is proportional
to the silicon temperature.

This patch provides a platform driver which expose this feature.
It is moduled as a MFD child of the System Control Module core
MFD driver.

This driver provides only APIs to access the device properties,
like temperature, thresholds and update rate.

Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: J Keerthy <j-keerthy@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>