arm64: zynqmp: Enable usb mass storage command and functionality

Enable ums command for zcu100 to enable mass storage gadget.
Tested with ums 0 mmc 0 (for SD) and ums 0 usb 0 (for USB flashdisk).

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/xilinx_zynqmp_zcu100_revC_defconfig b/configs/xilinx_zynqmp_zcu100_revC_defconfig
index 7ddb835..154fffb 100644
--- a/configs/xilinx_zynqmp_zcu100_revC_defconfig
+++ b/configs/xilinx_zynqmp_zcu100_revC_defconfig
@@ -34,6 +34,7 @@
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SPI=y
 CONFIG_CMD_USB=y
+CONFIG_CMD_USB_MASS_STORAGE=y
 CONFIG_CMD_TFTPPUT=y
 CONFIG_CMD_TIME=y
 CONFIG_MP=y