thermal: imx_tmu: enable monitoring and default alert/critical

thermal: imx_tmu: enable monitoring and default alert/critical

Set default critical/alert temperature and enabling monoitoring.

Without calling imx_tmu_enable_msite() monitoring will not be enabled
and read_temperature will return 0. Additionally without setting alert
temperature will cause imx_tmu_get_temp() to spin indefiniately thinking
the system needs to cool.

This resolves the board spinning endlessly when enabling IMX_TMU in the
SPL.

Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Tim Harvey <tharvey@gateworks.com>