mfd: twl4030: simplified child creation code

Minor cleanup to twl4030-core: define a helper function to populate
a single child node, and use it to replace six inconsistent versions
of the same logic.  Both object and source code shrink.

As part of this, some devices now have more IRQ resources:  battery
charger, keypad, ADC, and USB transceiver.  That helps to remove some
irq #defines that block the children's drivers code from compiling on
non-OMAP platforms.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>