twl: create regulator devices

twl: create regulator devices

Initial code to create twl4030 voltage regulator devices, using
the new regulator framework.  Note that this now starts to care
what name is used to declare the TWL chip:

 - TWL4030 is the "old" chip; newer ones have a bigger variety
   of VAUX2 voltages.

 - The tps65930 and tps65920 are cost-reduced catalog versions of
   the TWL5030 parts ... fewer regulators, no BCI, etc.  (Rev C
   Beagles were anticipated to use '930 parts...)

Board-specific regulator configuration should be provided, listing
which regulators are used and their constraints (e.g. 1.8V only).

Code that could ("should"?) leverage the regulator stuff includes
twl4030 USB transceiver support and MMC glue, LCD support for the
3430SDP and Labrador boards, and S-Video output.

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