linux-phytec-fsl

phy: twl4030-usb: add ABI documentation

This driver device one local attribute: vbus.
Describe that in Documentation/ABI/testing/sysfs-platform/twl4030-usb.

Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>