dma-helpers: allow including from target-independent code

Target-independent code cannot construct sglists, but it can take
them from the outside as a black box.  Allow this.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

dma.h

@@ -15,10 +15,13 @@
 #include "hw/hw.h"
 #include "block.h"
 
-typedef struct {
+typedef struct ScatterGatherEntry ScatterGatherEntry;
+
+#if defined(TARGET_PHYS_ADDR_BITS)
+struct ScatterGatherEntry {
     target_phys_addr_t base;
     target_phys_addr_t len;
-} ScatterGatherEntry;
+};
 
 struct QEMUSGList {
     ScatterGatherEntry *sg;
@@ -31,6 +34,7 @@ void qemu_sglist_init(QEMUSGList *qsg, int alloc_hint);
 void qemu_sglist_add(QEMUSGList *qsg, target_phys_addr_t base,
                      target_phys_addr_t len);
 void qemu_sglist_destroy(QEMUSGList *qsg);
+#endif
 
 typedef BlockDriverAIOCB *DMAIOFunc(BlockDriverState *bs, int64_t sector_num,
                                  QEMUIOVector *iov, int nb_sectors,