s390x/kvm: make printf always compile in debug output

Wrapped printf calls inside debug macros (DPRINTF) in `if` statement.
This will ensure that printf function will always compile even if debug
output is turned off and, in turn, will prevent bitrot of the format
strings.

Signed-off-by: Danil Antonov <g.danil.anto@gmail.com>
Message-Id: <CA+KKJYAhsuTodm3s2rK65hR=-Xi5+Z7Q+M2nJYZQf2wa44HfOg@mail.gmail.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
