thermal: OMAP3/DM3730 band gap thermal sensor driver

Could have used ti-soc-thermal framework, but it's too much work to
backport it to 3.2 and it's DT only, so here is a standalone driver.

Note that proper hwmod data is needed for this driver to work
(more specifically runtime_pm to be able to control the clock).

diff --cc drivers/thermal/Kconfig
Simple merge

diff --cc drivers/thermal/Makefile
Simple merge

diff --cc drivers/thermal/omap3_thermal.c
Simple merge