MAINTAINERS: update maintainer entry for pxa/hx4700

Add Paul Parsons as maintainer for pxa/hx4700.
Also, add a mailing list and update the files.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Acked-by: Paul Parsons <lost.distance@yahoo.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>