CHROMIUMOS: thermal:exynos: enable HW overtemp poweroff on exynos5

CHROMIUMOS: thermal:exynos: enable HW overtemp poweroff on exynos5

Based on Doug Anderson's proposal for u-boot/exynos5 support:
    https://gerrit.chromium.org/gerrit/#change,25164

The new code checks if FW enables the HW overtemp poweroff.
If so, new code verifies the kernel shutdown threshold is a
lower temp than HW thermal poweroff temp and may set the kernel
shutdown to a lower temp.

If FW did not set the HW overtemp, we now set the poweroff threshhold
to 110C (previously was the kernel shutdown threshold).

Just to be painfully clear: "Shutdown" means kernel issues "shutdown"
request which may take several seconds to poweroff gracefully.
"Poweroff" means HW will "abruptly" kill power to the system.

BUG=chrome-os-partner:9945
TEST=manual testing with heat gun and running:
	while true; do md5sum /boot/* ; done

Change-Id: I93e0a3e6e301cccd9ddd939d20d632b0e01e393f
Signed-off-by: Grant Grundler <grundler@chromium.org>
Reviewed-on: https://gerrit-int.chromium.org/20668
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>
Tested-by: Bernie Thompson <bhthompson@chromium.org>
Reviewed-by: Grant Grundler <grundler@google.com>
Tested-by: Grant Grundler <grundler@google.com>
Commit-Ready: Grant Grundler <grundler@google.com>