target: Use CPUArchState as interface to target-specific CPU state

target: Use CPUArchState as interface to target-specific CPU state

While CPUState is our interface with generic code, CPUArchState is
our interface with target-specific code. Use CPUArchState as an
abstract type, defined by each target.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220214183144.27402-13-f4bug@amsat.org>