freescale: pblimage: refactor CONFIG_SYS_FSL_PBL_{PBI, RCW}

Pull out "$(SRCTREE)/" from CONFIG_SYS_FSL_PBL_PBI
and CONFIG_SYS_FSL_PBL_RCW and push it into the top Makefile.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: York Sun <yorksun@freescale.com>
Cc: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Cc: Valentin Longchamp <valentin.longchamp@keymile.com>
diff --git a/Makefile b/Makefile
index 0df3780..198efa3 100644
--- a/Makefile
+++ b/Makefile
@@ -805,8 +805,8 @@
 MKIMAGEFLAGS_u-boot.kwb = -n $(CONFIG_SYS_KWD_CONFIG) -T kwbimage \
 		-a $(CONFIG_SYS_TEXT_BASE) -e $(CONFIG_SYS_TEXT_BASE)
 
-MKIMAGEFLAGS_u-boot.pbl = -n $(CONFIG_SYS_FSL_PBL_RCW) \
-		-R $(CONFIG_SYS_FSL_PBL_PBI) -T pblimage
+MKIMAGEFLAGS_u-boot.pbl = -n $(srctree)/$(CONFIG_SYS_FSL_PBL_RCW:"%"=%) \
+		-R $(srctree)/$(CONFIG_SYS_FSL_PBL_PBI:"%"=%) -T pblimage
 
 u-boot.img u-boot.kwb u-boot.pbl: u-boot.bin FORCE
 	$(call if_changed,mkimage)