mfd: TWL4030 core driver

mfd: TWL4030 core driver

This patch adds the core of the TWL4030 driver, which supports
chips including the TPS65950.  These chips are multi-function; see

  http://focus.ti.com/docs/prod/folders/print/tps65950.html

Public specs are in the works.  For now, the block diagram on
the second page of the datasheet is fairly informative.

There are some known issues with this core code.  Most notably,
the IRQ dispatching needs simplification (to use more of genirq),
generalization (integrating support for secondary IRQ dispatch
as well as primary, and removing the build dependency on OMAP),
and then probably updating to leverage threaded IRQ support
(expected to arrive in mainline "soon").

Once the core is in mainline, drivers for other parts of this
chip can follow its lead and start swimming upstream too.

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