Not functional printk in ME

[daniel-rossier]

It seems that printk() - in a probe function - is not working when a ME is automatically injected by the agency app while it is working when injected manually.

[daniel-rossier]

With refso3 and printk() executed in vdummy/probe(), it is displayed correctly.
I noticed that vuart is not used along printk() execution. This needs to be adapted (will be in this issue).

[daniel-rossier]

The problem was due to recent upgrades of SO3 where a test against CONFIG_SOO was missing in serial_write().
@BasileCuneo @jmi-reds Please make a test with these changes although it should not affect the behaviour.