INTERNAL: config: Use step_wise governor for thermal

Change the default thermal governor to step_wise instead of
power allocator for thermal throttling to work

BUG=b:126413994
Test=Run tests to allow CPU reach its passive trips and
observe the current CPU frequency drop to the lowest OPP.
When CPU gets cooled the CPU frequency will be back to highest OPP.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Khasim Syed Mohammed <khasim.mohammed@linaro.org>
Change-Id: I516526ab7540662b1647de757db9d1bcdc41f44f