target: Move ArchCPUClass definition to 'cpu.h'

target: Move ArchCPUClass definition to 'cpu.h'

The OBJECT_DECLARE_CPU_TYPE() macro forward-declares each
ArchCPUClass type. These forward declarations are sufficient
for code in hw/ to use the QOM definitions. No need to expose
these structure definitions. Keep each local to their target/
by moving them to the corresponding "cpu.h" header.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20231013140116.255-13-philmd@linaro.org>