dm: usb: sandbox: Enable USB

Enable USB emulation and associated features so that USB can be used in
sandbox.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 93bcf46..6ce1f0a 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -12,3 +12,7 @@
 CONFIG_PCI=y
 CONFIG_DM_PCI=y
 CONFIG_PCI_SANDBOX=y
+CONFIG_USB=y
+CONFIG_DM_USB=y
+CONFIG_USB_EMUL=y
+CONFIG_USB_STORAGE=y