mfd: Fix twl4030 boot with twl4030 usb transceiver enabled

The usb regulator supplies (usb1v5, usb1v8 & usb3v1) must be available
before adding the twl4030_usb child, else twl4030_usb_ldo_init() will
always fail thus causing boot lock-up.

This patch fixes boot on OMAP systems using the twl4030 usb transceiver.
CONFIG_TWL4030_USB=y

Signed-off-by: Roger Quadros <ext-roger.quadros@nokia.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>