ARM: pxa: use module_platform_driver macro

This patch removes some code duplication by using
module_platform_driver.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Olof Johansson <olof@lixom.net>