OMAP4470: TEMP_SENSOR: Fatal threshold hardware warm reset generation

On 4470 the TSHUT signal can be mapped to the device SCRM external
warm reset logic to activate the PRM.SYS_WARMIN_RST input
when a fatal temperature threshold (TSHUT_HOT) is exceeded.
Hence, a hardware warm reset can be triggered directly on
the device upon a fatal temperature threshold crossing event.

Since this feature have been added for 4470, shutdown thresholds
can be set earlier. So, additional checking has been added to prevent
multiple writing to one time writable register.

Also this patch add corresponding sysfs debug hook functions to
enable/disable hardware reset feature.

Signed-off-by: Leonid Iziumtsev <x0153368@ti.com>
Change-Id: I260e16e2808fddc0ecb06211a74aced8c4b12a5d