spl: support loading from UBI volumes

Add support for loading from UBI volumes on the top of NAND
and OneNAND.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/common/spl/Makefile b/common/spl/Makefile
index 2e0f695..b15f0f6 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -13,8 +13,11 @@
 obj-$(CONFIG_SPL_LOAD_FIT) += spl_fit.o
 obj-$(CONFIG_SPL_NOR_SUPPORT) += spl_nor.o
 obj-$(CONFIG_SPL_YMODEM_SUPPORT) += spl_ymodem.o
+ifndef CONFIG_SPL_UBI
 obj-$(CONFIG_SPL_NAND_SUPPORT) += spl_nand.o
 obj-$(CONFIG_SPL_ONENAND_SUPPORT) += spl_onenand.o
+endif
+obj-$(CONFIG_SPL_UBI) += spl_ubi.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