spl: common: Support for USB MSD FAT image loading

Add SPL support to be able to detect a USB Mass Storage device
connected to a USB host.  Once a USB Mass storage device is detected
the SPL will load the u-boot.img from a FAT partition to target address.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
diff --git a/common/spl/Makefile b/common/spl/Makefile
index c8d5963..65a1484 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -16,5 +16,6 @@
 obj-$(CONFIG_SPL_ONENAND_SUPPORT) += spl_onenand.o
 obj-$(CONFIG_SPL_NET_SUPPORT) += spl_net.o
 obj-$(CONFIG_SPL_MMC_SUPPORT) += spl_mmc.o
+obj-$(CONFIG_SPL_USB_SUPPORT) += spl_usb.o
 obj-$(CONFIG_SPL_FAT_SUPPORT) += spl_fat.o
 endif