qemu-system-nios2 not working on s390x (big endian) hosts
Description of problem:
qemu-system-nios2 fails to boot a Linux kernel on s390x hosts.
Steps to reproduce:
1. wget https://qemu-advcal.gitlab.io/qac-best-of-multiarch/download/day14.tar.xz
2. tar -xJf day14.tar.xz 
3. cd day14/
4. qemu-system-nios2 -nographic -kernel vmlinux.elf
Additional information:
When running with "-d in_asm", it seems like the code initially starts executing ok, but in one of the early translation blocks, there is a difference when comparing the log with a run from a x86 host:

```
IN: fdt_check_header
0xc81afd48:  ldw	r3,0(r4)
0xc81afd4c:  srli	r5,r3,24
0xc81afd50:  slli	r2,r3,24
0xc81afd54:  or	r2,r2,r5
0xc81afd58:  slli	r5,r3,8
0xc81afd5c:  srli	r3,r3,8
0xc81afd60:  andhi	r5,r5,255
0xc81afd64:  andi	r3,r3,65280
0xc81afd68:  or	r2,r2,r5
0xc81afd6c:  or	r2,r2,r3
0xc81afd70:  movhi	r3,53262
0xc81afd74:  addi	r3,r3,-275
0xc81afd78:  bne	r2,r3,0xc81afde8
```

On the x86 host, the branch at the end is not taken, while on the s390x host, the branch is taken.