usb: Make USB_VBUS_GPIO a Kconfig option

Previously we had a set of magic #define's in board.h that would both
enable and set the GPIO controller & pin if a given board used a GPIO
for USB VBUS.  Now we make it a proper Kconfig set of options that
specify if the feature is needed, the GPIO controller device name, and
pin number.  In the future this should move to devicetree.

Updated the related boards that used this feature to set the Kconfig
options in the Kconfig.defconfig

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>