Fast creation and deletion of OpenAMP sessions crashes slave system

The slave system crashes after a couple of create/delete operations of OpenAMP sessions. The root cause is that background print buffer allocated in constructor of Comm class is not freed when the object is deleted.

Command list to validate the fix:

echo on
openamp create a
openamp create b
openamp create c
openamp create d
openamp delete j
openamp create e
openamp delete e
openamp create f
openamp delete f
openamp create g
openamp delete g
openamp create h
openamp delete h
openamp create i
openamp delete i
openamp create j
openamp console j stat