Makefile: Add more files to clean list

When building for i.mx8m boards with binman, a few more additional
files are created which should be removed when running 'make clean'

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/Makefile b/Makefile
index 95afb98..58a0c34 100644
--- a/Makefile
+++ b/Makefile
@@ -2184,7 +2184,9 @@
 	       u-boot* MLO* SPL System.map fit-dtb.blob* \
 	       u-boot-ivt.img.log u-boot-dtb.imx.log SPL.log u-boot.imx.log \
 	       lpc32xx-* bl31.c bl31.elf bl31_*.bin image.map tispl.bin* \
-	       idbloader.img flash.bin flash.log defconfig keep-syms-lto.c
+	       idbloader.img flash.bin flash.log defconfig keep-syms-lto.c \
+	       mkimage-out.spl.mkimage mkimage.spl.mkimage imx-boot.map \
+	       itb.fit.fit itb.fit.itb itb.map spl.map
 
 # Directories & files removed with 'make mrproper'
 MRPROPER_DIRS  += include/config include/generated spl tpl \