TWL4030 Add power reset button

The Zoom2 power reset button is on the top right side of the
main board.  Press and hold for about to 8 seconds to completely
reset the board.

Some of the beta boards have a hardware problem that prevents
using this feature.  If is difficult to further characterize the
boards that fail.  So disable resetting for all beta boards.

The Zoom1 reset button is the red circle on the top right,
front of the board.  Press and hold the button for 8 seconds to
completely reset the board.

After analyzing beagle, it was determined that other boards
that use the twl4030 for power managment can also make use
this function.

The resetting is done by the power management part of the twl4030.
Since there is no existing drivers/power, add one.

The compilation of power/twl4030.h is controlled by the config
variable CONFIG_TWL4030_POWER

Signed-off-by: Tom Rix <Tom.Rix@windriver.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Heiko Schocher <hs@denx.de>