MX28: config: Allow different target generation in elftosb call

The elftosb call needs to use a target param specific for i.MX28. This
patch allow for later addition of i.MX233.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Acked-by: Marek Vasut <marex@denx.de>

Makefile

@@ -461,8 +461,11 @@ $(obj)u-boot.ais:       $(obj)spl/u-boot-spl.bin $(obj)u-boot.bin
 		cat $(obj)spl/u-boot-spl-pad.ais $(obj)u-boot.bin > \
 			$(obj)u-boot.ais
 
+# Specify the target for use in elftosb call
+ELFTOSB_TARGET-$(CONFIG_MX28) = imx28
+
 $(obj)u-boot.sb:       $(obj)u-boot.bin $(obj)spl/u-boot-spl.bin
-		elftosb -zdf imx28 -c $(TOPDIR)/$(CPUDIR)/$(SOC)/u-boot.bd \
+		elftosb -zdf $(ELFTOSB_TARGET-y) -c $(TOPDIR)/$(CPUDIR)/$(SOC)/u-boot-$(ELFTOSB_TARGET-y).bd \
 			-o $(obj)u-boot.sb
 
 # On x600 (SPEAr600) U-Boot is appended to U-Boot SPL.