thermal/drivers/imx8mm: Enable ADC when enabling monitor

The i.MX 8MP has a ADC_PD bit in the TMU_TER register that controls the
operating mode of the ADC:
* 0 means normal operating mode
* 1 means power down mode

When enabling/disabling the TMU, the ADC operating mode must be set
accordingly.

i.MX 8M Mini & Nano are lacking this bit.

Signed-off-by: Paul Gerber <Paul.Gerber@tq-group.com>
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Fixes: 2b8f1f03 ("thermal: imx8mm: Add i.MX8MP support")
Link: https://lore.kernel.org/r/20211122114225.196280-1-alexander.stein@ew.tq-group.com


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>