memory.h: Move MemTxResult type to memattrs.h

Move the MemTxResult type to memattrs.h. We're going to want to
use it in cpu/qom.h, which doesn't want to include all of
memory.h. In practice MemTxResult and MemTxAttrs are pretty
closely linked since both are used for the new-style
read_with_attrs and write_with_attrs callbacks, so memattrs.h
is a reasonable home for this rather than creating a whole
new header file for it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>

include/exec/memory.h

@@ -112,16 +112,6 @@ static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
     n->end = end;
 }
 
-/* New-style MMIO accessors can indicate that the transaction failed.
- * A zero (MEMTX_OK) response means success; anything else is a failure
- * of some kind. The memory subsystem will bitwise-OR together results
- * if it is synthesizing an operation from multiple smaller accesses.
- */
-#define MEMTX_OK 0
-#define MEMTX_ERROR             (1U << 0) /* device returned an error */
-#define MEMTX_DECODE_ERROR      (1U << 1) /* nothing at that address */
-typedef uint32_t MemTxResult;
-
 /*
  * Memory region callbacks
  */