Makefile: Add possibility to set entry-point for u-boot.img

This patch enabled boards using the SPL framework to set
an entry point in the U-Boot mkimage image "u-boot.img".
Until now the entry point in the header has been set to 0.
By setting CONFIG_SYS_UBOOT_START in the board header, boards
can override this default location.

This will be used by the upcoming a3m071 MPC5200 board port.

Signed-off-by: Stefan Roese <sr@denx.de>

Makefile

@@ -450,9 +450,18 @@ $(obj)u-boot.ldr.hex:	$(obj)u-boot.ldr
 $(obj)u-boot.ldr.srec:	$(obj)u-boot.ldr
 		$(OBJCOPY) ${OBJCFLAGS} -O srec $< $@ -I binary
 
+#
+# U-Boot entry point, needed for booting of full-blown U-Boot
+# from the SPL U-Boot version.
+#
+ifndef CONFIG_SYS_UBOOT_START
+CONFIG_SYS_UBOOT_START := 0
+endif
+
 $(obj)u-boot.img:	$(obj)u-boot.bin
 		$(obj)tools/mkimage -A $(ARCH) -T firmware -C none \
-		-O u-boot -a $(CONFIG_SYS_TEXT_BASE) -e 0 \
+		-O u-boot -a $(CONFIG_SYS_TEXT_BASE) \
+		-e $(CONFIG_SYS_UBOOT_START) \
 		-n $(shell sed -n -e 's/.*U_BOOT_VERSION//p' $(VERSION_FILE) | \
 			sed -e 's/"[	 ]*$$/ for $(BOARD) board"/') \
 		-d $< $@