exec: hide mr->ram_addr from qemu_get_ram_ptr users

Let users of qemu_get_ram_ptr and qemu_ram_ptr_length pass in an
address that is relative to the MemoryRegion.  This basically means
what address_space_translate returns.

Because the semantics of the second parameter change, rename the
function to qemu_map_ram_ptr.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/memory.c b/memory.c
index f8085ea..8ba496d 100644
--- a/memory.c
+++ b/memory.c
@@ -1657,10 +1657,10 @@
         mr = mr->alias;
     }
     assert(mr->ram_block);
-    ptr = qemu_get_ram_ptr(mr->ram_block, memory_region_get_ram_addr(mr));
+    ptr = qemu_map_ram_ptr(mr->ram_block, offset);
     rcu_read_unlock();
 
-    return ptr + offset;
+    return ptr;
 }
 
 MemoryRegion *memory_region_from_host(void *ptr, ram_addr_t *offset)