spl: support for booting via usbeth

In case of usbeth booting just call net_load_image("usb_ether").
This patch also adds CONFIG_SPL_USBETH_SUPPORT and
CONFIG_SPL_MUSB_NEW_SUPPORT config options to enable linking of SPL
against USB gagdet support and new MUSB driver resp.

Signed-off-by: Ilya Yanok <ilya.yanok@cogentembedded.com>
diff --git a/spl/Makefile b/spl/Makefile
index 101d478..aac6146 100644
--- a/spl/Makefile
+++ b/spl/Makefile
@@ -81,6 +81,8 @@
 LIBS-$(CONFIG_SPL_NET_SUPPORT) += net/libnet.o
 LIBS-$(CONFIG_SPL_ETH_SUPPORT) += drivers/net/libnet.o
 LIBS-$(CONFIG_SPL_ETH_SUPPORT) += drivers/net/phy/libphy.o
+LIBS-$(CONFIG_SPL_MUSB_NEW_SUPPORT) += drivers/usb/musb-new/libusb_musb-new.o
+LIBS-$(CONFIG_SPL_USBETH_SUPPORT) += drivers/usb/gadget/libusb_gadget.o
 
 ifneq ($(CONFIG_AM33XX)$(CONFIG_OMAP34XX)$(CONFIG_OMAP44XX)$(CONFIG_OMAP54XX),)
 LIBS-y += $(CPUDIR)/omap-common/libomap-common.o