ARM: omap2plus_defconfig: Enable more droid4 devices as loadable modules

Droid4 needs USB option serial driver for modem, and lm3532 for the
LCD backlight.

Note that the LCD backlight does not yet get enabled automatically,
but needs to be done manually with:

# echo 50 > /sys/class/leds/lm3532::backlight/brightness

Signed-off-by: Tony Lindgren <tony@atomide.com>