s390x/ipl: Try to detect Linux vs non Linux for initial IPL PSW

s390x/ipl: Try to detect Linux vs non Linux for initial IPL PSW

Right now the IPL device always starts from address 0x10000 (the usual
Linux entry point). To run other guests (e.g. test programs) it is
useful to use the IPL PSW from address 0. We can use the Linux magic
at 0x10008 to decide.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20180612125933.262679-1-borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>