ARM: omap2plus_defconfig: enable twl4030_madc as a loadable module

The ADC is used by twl4030_charger to read voltages. If a dtb contains
the ADC but the module is not build, probing twl4030_charger will be
endlessly deferred, so just enable CONFIG_TWL4030_MADC in the config.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Tony Lindgren <tony@atomide.com>