MAINTAINERS: update pxa and mmp

Merge PXA168, PXXA910 and MMP2 together. Add Haojian as maintainer of
both arch-pxa and arch-mmp. Haojian's git tree is also added.

Update Eric's tree since the original one is obsolte.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>