ARM: ux500: Provide a supply name for the AB8500 AUX regulators to use

AB8500 AUX regulators are supplied by EXT3 on some boards. This supply
phandle lookup will enable the regulator core to search for and locate
the EXT3 supply at registration time.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>