system/physmem: Replace qemu_mutex_lock() calls with QEMU_LOCK_GUARD

system/physmem: Replace qemu_mutex_lock() calls with QEMU_LOCK_GUARD

Simplify cpu_[un]register_map_client() and cpu_notify_map_clients()
by replacing the pair of qemu_mutex_lock/qemu_mutex_unlock calls by
the WITH_QEMU_LOCK_GUARD() macro.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Mattias Nissler <mnissler@rivosinc.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20240507123025.93391-2-philmd@linaro.org>