Unable to set SVE VL to 1024 bits or above since 7b6a2198

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1906536
Reported by 'Alex Coplan' on 2020-12-02 :

Prior to 7b6a2198e71794c851f39ac7a92d39692c786820, the QEMU option sve-
max-vq could be used to set the vector length of the implementation. This
is useful (among other reasons) for testing software compiled with a fixed
SVE vector length. Since this commit, the vector length is capped at 512
bits.

To reproduce the issue:

$ cat rdvl.s
.global _start
_start:
  rdvl x0, #1
  asr x0, x0, #4
  mov x8, #93 // exit
  svc #0
$ aarch64-linux-gnu-as -march=armv8.2-a+sve rdvl.s -o rdvl.o
$ aarch64-linux-gnu-ld rdvl.o
$ for vl in 1 2 4 8 16; do ../build-qemu/aarch64-linux-user/qemu-aarch64
-cpu max,sve-max-vq=$vl a.out; echo $?; done
1
2
4
4
4

For a QEMU built prior to the above revision, we get the output:
1
2
4
8
16

as expected. It seems that either the old behavior should be restored, or
there should be an option to force a higher vector length?