ARM: mmp: append CONFIG_MACH_MMP2_DT

Append CONFIG_MACH_MMP2_DT.

CONFIG_MACH_MMP_DT is used to ARMv5 DT support. CONFIG_MACH_MMP2_DT
is used to ARMv7 DT support. These two machine support can't be
selected at the same time.

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