migration: Make dirtyrate.c target independent

After the previous two patches, there is nothing else that is target
specific.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230511141208.17779-6-quintela@redhat.com>
2 files changed