ARM: configs: bcm_defconfig: enable bcm590xx regulator support

Enable BCM590xx MFD and regulator drivers to manage voltage
regulators on BCM281xx platforms.

Signed-off-by: Tim Kryger <tim.kryger@linaro.org>
Signed-off-by: Matt Porter <mporter@linaro.org>
Reviewed-by: Markus Mayer <markus.mayer@linaro.org>