imx8mm_evk_defconfig: Select CONFIG_IMX_TMU

Select the i.MX8MM thermal driver as it is useful for displaying
the CPU temperature and its grading:

CPU:   Commercial temperature grade (0C to 95C) at 38C

It also prevents booting when the temperature is above the alert
point.

Signed-off-by: Fabio Estevam <festevam@denx.de>
diff --git a/configs/imx8mm_evk_defconfig b/configs/imx8mm_evk_defconfig
index ac9810f..822c2fb 100644
--- a/configs/imx8mm_evk_defconfig
+++ b/configs/imx8mm_evk_defconfig
@@ -104,6 +104,7 @@
 CONFIG_SYSRESET_PSCI=y
 CONFIG_SYSRESET_WATCHDOG=y
 CONFIG_DM_THERMAL=y
+CONFIG_IMX_TMU=y
 CONFIG_USB=y
 CONFIG_SPL_USB_HOST=y
 CONFIG_USB_EHCI_HCD=y