s390x/mmu: ASC selection in s390_cpu_get_phys_page_debug()

s390x/mmu: ASC selection in s390_cpu_get_phys_page_debug()

Let's select the ASC before calling the function. This is a prepararion
to remove the ASC magic depending on the access mode from mmu_translate.

There is currently no way to distinguish if we have code or data access.
For now, we were using code access, because especially when debugging with
the gdbstub, we want to read and disassemble what we single-step.

Note: KVM guest can now no longer be crashed using qmp/hmp/gdbstub if they
happen to be in AR mode.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190816084708.602-3-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>