ARM: multi_v7_defconfig: Select CONFIG_MACH_BERLIN_BG2Q

Now that we support Berlin BG2Q, select CONFIG_MACH_BERLIN_BG2Q so that we can
boot BG2Q based boards like the BG2Q DMP.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Olof Johansson <olof@lixom.net>