thermal: add imx thermal driver support

This is based on the initial imx thermal work done by
Rob Lee <rob.lee@linaro.org> (Not sure if the email address is still
valid).  Since he is no longer interested in the work and I have
rewritten a significant amount of the code, I just took the authorship
over from him.

It adds the imx thermal support using Temperature Monitor (TEMPMON)
block found on some Freescale i.MX SoCs.  The driver uses syscon regmap
interface to access TEMPMON control registers and calibration data, and
supports cpufreq as the cooling device.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>