move QEMUSGList typedef

Move the QEMUSGList typedef to qemu-common so it can easily be used.
The actual struct definition stays in dma.h.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/qemu-common.h b/qemu-common.h
index 1e3c665..c7064d3 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -270,6 +270,7 @@
 typedef struct SSIBus SSIBus;
 typedef struct EventNotifier EventNotifier;
 typedef struct VirtIODevice VirtIODevice;
+typedef struct QEMUSGList QEMUSGList;
 
 typedef uint64_t pcibus_t;