ARM: dts: qcom: pm8941: add 5vs2 regulator node

pm8941 is missing the 5vs2 regulator node so let's add it since its
needed to get the external display working. This regulator was already
configured in the interrupts property on the parent node.

Note that this regulator is referred to as mvs2 in the downstream MSM
kernel sources.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>