S390: Add stub for cpu_get_phys_page_debug

We don't implement any virtual memory in the S390 target so far, so let's
add a stub for this now mandatory function.

Fixes building of S390 target.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

target-s390x/helper.c

diff --git a/target-s390x/helper.c b/target-s390x/helper.c
index ba0c052..4a5297b 100644
--- a/target-s390x/helper.c
+++ b/target-s390x/helper.c
@@ -58,6 +58,11 @@
     tlb_flush(env, 1);
 }
 
+target_phys_addr_t cpu_get_phys_page_debug(CPUState *env, target_ulong addr)
+{
+    return 0;
+}
+
 #ifndef CONFIG_USER_ONLY
 
 int cpu_s390x_handle_mmu_fault (CPUState *env, target_ulong address, int rw,