pinctrl: pm8994: add pad voltage regulator defines

This patch adds defines for internal voltage regulators used
to switch voltage levels on gpio/mpp pads.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>