microblaze: Support the latest mmu-kernel stat64 ABI.

Microblaze recently changed their ABI. The new is not backwards compatible
and there doesn't seem to be a way to distinguish old/new binaries.
Let's support the latest ABI for now and hope someone figures out a way to
hande both ABI's later.
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>

linux-user/syscall_defs.h

@@ -1231,10 +1231,11 @@ struct __attribute__((__packed__)) target_stat64 {
 	uint32_t st_uid;
 	uint32_t st_gid;
 	uint64_t st_rdev;
-	uint32_t __pad2;
+	uint64_t __pad1;
 
 	int64_t  st_size;
-	int32_t st_blksize;
+	int32_t  st_blksize;
+	uint32_t __pad2;
 	int64_t st_blocks;	/* Number 512-byte blocks allocated. */
 
 	int	       target_st_atime;