s390x/mmu: Skip exceptions properly when translating addresses for debug

When a fault occurs during the MMU lookup in s390_cpu_get_phys_page_debug(),
the trigger_page_fault() function writes the translation exception code
into the lowcore - something you would not expect during a memory access
by the debugger. Ease this problem by adding an additional parameter to
mmu_translate() which can be used to specify whether a program check and
the translation exception code should be injected or not.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
