Convert CONFIG_TWL4030_USB to Kconfig

This converts the following to Kconfig:
   CONFIG_TWL4030_USB

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/drivers/usb/Kconfig b/drivers/usb/Kconfig
index 13e9e49..7de4105 100644
--- a/drivers/usb/Kconfig
+++ b/drivers/usb/Kconfig
@@ -57,6 +57,8 @@
 
 source "drivers/usb/emul/Kconfig"
 
+source "drivers/usb/phy/Kconfig"
+
 source "drivers/usb/ulpi/Kconfig"
 
 comment "USB peripherals"