ARM: dts: OMAP4460: Thermal: Add slope and offset values

Currently the slope and offset values for calculating the
hot spot temperature of a particular thermal zone is part
of driver data. Pass them here instead and obtain the values
while of node parsing.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>