MAINTAINERS: Assign some more files in the hw/arm/ directory

MAINTAINERS: Assign some more files in the hw/arm/ directory

I apparently missed some more files and even a complete machine (the
"imx25-pdk") in my previous patch... but now we should hopefully have
a completely coverage for all available ARM boards.

Fixes: 95a5db3ae5698b49c63144610ad02913e780c828
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 1542782568-20059-1-git-send-email-thuth@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>