arm: mxs: Preprocess u-boot.bd so they contain full path

The u-boot-imx23.bd and u-boot-imx28.bd need to be preprocessed, otherwise
they have issues with out-of-tree build where elftosb tool couldn't sometimes
find the u-boot.bin and spl/u-boot-spl.bin .

Preprocess these .bd files with sed and insert full path to u-boot.bin and
spl/u-boot-spl.bin to prevent this issue. Moreover, to avoid adding more
churn into main Makefile, move all this preprocessing and u-boot.sb generation
into CPU directory instead.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
diff --git a/Makefile b/Makefile
index d1d286b..dd7e02a 100644
--- a/Makefile
+++ b/Makefile
@@ -512,13 +512,9 @@
 		cat $(obj)spl/u-boot-spl-pad.ais $(obj)u-boot.img > \
 			$(obj)u-boot.ais
 
-# Specify the target for use in elftosb call
-ELFTOSB_TARGET-$(CONFIG_MX23) = imx23
-ELFTOSB_TARGET-$(CONFIG_MX28) = imx28
 
 $(obj)u-boot.sb:       $(obj)u-boot.bin $(obj)spl/u-boot-spl.bin
-		elftosb -zf $(ELFTOSB_TARGET-y) -c $(TOPDIR)/$(CPUDIR)/$(SOC)/u-boot-$(ELFTOSB_TARGET-y).bd \
-			-o $(obj)u-boot.sb
+		$(MAKE) -C $(SRCTREE)/$(CPUDIR)/$(SOC)/ $(OBJTREE)/u-boot.sb
 
 # On x600 (SPEAr600) U-Boot is appended to U-Boot SPL.
 # Both images are created using mkimage (crc etc), so that the ROM
@@ -849,6 +845,7 @@
 	@rm -f $(obj)u-boot.ais
 	@rm -f $(obj)u-boot.dtb
 	@rm -f $(obj)u-boot.sb
+	@rm -f $(obj)u-boot.bd
 	@rm -f $(obj)u-boot.spr
 	@rm -f $(obj)nand_spl/{u-boot.{lds,lst},System.map}
 	@rm -f $(obj)nand_spl/{u-boot-nand_spl.lds,u-boot-spl,u-boot-spl.map}