Change Key/Certificate Storage to be in the Device Tree

[dayeol]

Currently, the boot loader is writing the attestation key and device certificate to the security monitor memory.
We need to add a device to the device tree and the security monitor should read out the key/certificate from the memory.
If the SM fails to probe the device, it should not register ecalls and show error messages instead.

[dayeol]

This was accidentally marked as resolved.