target/arm/hvf: Disable SME feature

target/arm/hvf: Disable SME feature

macOS 15.2's Hypervisor.framework exposes SME feature on M4 Macs.
However, QEMU's hvf accelerator code does not properly support it
yet, causing QEMU to fail to start when hvf accelerator is used on
these systems, with the error message:

  qemu-aarch64-softmmu: cannot disable sme4224
  All SME vector lengths are disabled.
  With SME enabled, at least one vector length must be enabled.

Ideally we would have SME support on these hosts; however, until that
point, we must suppress the SME feature in the ID registers, so that
users can at least run non-SME guests.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2665
Signed-off-by: Joelle van Dyne <j@getutm.app>
Message-id: 20250224165735.36792-1-j@getutm.app
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: expanded commit message, comment]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>