[ARM] mmp: add support for Marvell MMP2

Marvell MMP2 (aka ARMADA610) is a SoC based on PJ4 core. It's
ARMv6 compatible.  Support basic interrupt handler and timer,
and basic support for MMP2 based FLINT platform.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>