hvf: Add Apple Silicon support

With Apple Silicon available to the masses, it's a good time to add support
for driving its virtualization extensions from QEMU.

This patch adds all necessary architecture specific code to get basic VMs
working, including save/restore.

Known limitations:

  - WFI handling is missing (follows in later patch)
  - No watchpoint/breakpoint support

Signed-off-by: Alexander Graf <agraf@csgraf.de>
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20210916155404.86958-5-agraf@csgraf.de
[PMM: added missing #include]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>