ARM: berlin: select MFD_SYSCON by default

The chip and system controller nodes handle sub-devices, such as the
clock, pinctrl or reset controllers. The drivers handling them need a
regmap provided by syscon. Select it by default when using a Berlin SoC.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>