dt-bindings: thermal: Change devicetree optional properties

LMH DCVSh driver always expects the properties like interrupts, affinity
and reg as mandatory devicetree properties. The driver in certain
targets will have to just be probed with just isens regulator devicetree
properties with the others. In order to handle that make all the
properties as optional.

Change-Id: I0ccbd0f9ce511ca1e18bfbf8875c1e3fcfd46853