thermal: qoriq: Update the settings for TMUv2

For TMU v2, TMSAR registers need to be set properly to get the
accurate temperature values.
Also the temperature read needs to be converted to degree Celsius
since it is in degrees Kelvin.

Signed-off-by: Yuantian Tang <andy.tang@nxp.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200526060212.4118-1-andy.tang@nxp.com