Reported by Nikolaus Schaller, Aug 28, 2014

e.g.

drivers/phy/phy-twl4030-usb.c and drivers/power/twl4030_charger.c

which need void twl4030_charger_enable_usb_ext(bool enable)

This gives undefined symbol errors if the drivers are compiled as 
modules.
Therefore we need some other notification mechanism.

Why do we need to make this modules?

The GTA04 kernel should not only be optimized for OMAP3+TWL4030 but 
also for OMAP4+5.
For those we don't want to see a twl4030 driver compiled into the 
kernel.