gdbstub: Make syscall_complete/[gs]et_reg target-agnostic typedefs

gdbstub: Make syscall_complete/[gs]et_reg target-agnostic typedefs

Prototypes using gdb_syscall_complete_cb() or gdb_?et_reg_cb()
don't depend on "cpu.h", thus are not target-specific.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20221214143659.62133-1-philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230302190846.2593720-4-alex.bennee@linaro.org>
Message-Id: <20230303025805.625589-4-richard.henderson@linaro.org>