hvf: add guest debugging handlers for Apple Silicon hosts

hvf: add guest debugging handlers for Apple Silicon hosts

Guests can now be debugged through the gdbstub. Support is added for
single-stepping, software breakpoints, hardware breakpoints and
watchpoints. The code has been structured like the KVM counterpart.

While guest debugging is enabled, the guest can still read and write the
DBG*_EL1 registers but they don't have any effect.

Signed-off-by: Francesco Cagnin <fcagnin@quarkslab.com>
Message-id: 20230601153107.81955-5-fcagnin@quarkslab.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>