ARM: ux500: Provide SMSC911x fixed-regulator when not booting DT

The SMSC911x Ethernet chip requires a fixed-regulator in order to
function correctly. We have previously provided a means to obtain
this during a Device Tree boot, however nothing has been put into
place when booting with a non-DT kernel. This patch aims to change
that.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
[Added a Kconfig select so the build does not break]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>