accel: Rename 'hax_vcpu' as 'accel' in CPUState

All accelerators will share a single opaque context
in CPUState. Start by renaming 'hax_vcpu' as 'accel'.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230624174121.11508-7-philmd@linaro.org>
5 files changed