stat64 on sparc64 failed to get correct major/minor dev
Description of problem:
The reported device major/minor is not correct, e.g: stat /dev/zero:
Reported: Device type: 0,10500000
Correct : Device type: 1,5
Steps to reproduce:
1. "stat /dev/zero" or "ls -l /dev/zero"
Additional information:
The problem is a missing padding into target_stat64 struct related to sparc64. Here patch to solve the issue (it also fixes some incorrect variables size):

```
--- qemu-20230327/linux-user/syscall_defs.h	2023-03-27 15:41:42.000000000 +0200
+++ qemu-20230327/linux-user/syscall_defs.h.new	2023-03-27 21:43:25.615115126 +0200
@@ -1450,7 +1450,7 @@ struct target_stat {
 	unsigned int	st_dev;
 	abi_ulong	st_ino;
 	unsigned int	st_mode;
-	unsigned int	st_nlink;
+	short int	st_nlink;
 	unsigned int	st_uid;
 	unsigned int	st_gid;
 	unsigned int	st_rdev;
@@ -1465,8 +1465,7 @@ struct target_stat {
 
 #define TARGET_HAS_STRUCT_STAT64
 struct target_stat64 {
-	unsigned char	__pad0[6];
-	unsigned short	st_dev;
+	uint64_t	st_dev;
 
 	uint64_t	st_ino;
 	uint64_t	st_nlink;
@@ -1476,14 +1475,13 @@ struct target_stat64 {
 	unsigned int	st_uid;
 	unsigned int	st_gid;
 
-	unsigned char	__pad2[6];
-	unsigned short	st_rdev;
+	unsigned int	__pad0;
+	uint64_t	st_rdev;
 
         int64_t		st_size;
 	int64_t		st_blksize;
 
-	unsigned char	__pad4[4];
-	unsigned int	st_blocks;
+	int64_t		st_blocks;
 
 	abi_ulong	target_st_atime;
 	abi_ulong	target_st_atime_nsec;
@@ -1522,8 +1520,7 @@ struct target_stat {
 
 #define TARGET_HAS_STRUCT_STAT64
 struct target_stat64 {
-	unsigned char	__pad0[6];
-	unsigned short	st_dev;
+	uint64_t st_dev;
 
 	uint64_t st_ino;
 
@@ -1533,8 +1530,7 @@ struct target_stat64 {
 	unsigned int	st_uid;
 	unsigned int	st_gid;
 
-	unsigned char	__pad2[6];
-	unsigned short	st_rdev;
+	uint64_t        st_rdev;
 
 	unsigned char	__pad3[8];
```