target/s390x: Replace legacy cpu_physical_memory_[un]map() calls (2/3)

target/s390x: Replace legacy cpu_physical_memory_[un]map() calls (2/3)

Commit b7ecba0f6f6 ("docs/devel/loads-stores.rst: Document our
various load and store APIs") mentioned cpu_physical_memory_*()
methods are legacy, the replacement being address_space_*().

Replace the *_map() / *_unmap() methods in cpu_[un]map_lowcore().
No behavioral change expected.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20251002091132.65703-7-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>