arm: dts: imx8m*-u-boot: remove optional from tee-os entry

tee-os node is guarded by CONFIG_OPTEE. Since OPTEE adds driver support
for OP-TEE, the binary should then be packaged in the bootable image.
Remove the optional property to enforce this requirement.

Signed-off-by: Yannic Moog <y.moog@phytec.de>
4 files changed