usb: move CONFIG_USB_XHCI_DWC3 to Kconfig

Create an entry for "config USB_XHCI_DWC3" in Kconfig and
switch over to it for all boards.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/configs/ls2080ardb_defconfig b/configs/ls2080ardb_defconfig
index 82d14be..dc2b872 100644
--- a/configs/ls2080ardb_defconfig
+++ b/configs/ls2080ardb_defconfig
@@ -31,4 +31,5 @@
 CONFIG_FSL_DSPI=y
 CONFIG_USB=y
 CONFIG_USB_XHCI_HCD=y
+CONFIG_USB_XHCI_DWC3=y
 CONFIG_EFI_LOADER_BOUNCE_BUFFER=y