imx: Add u-boot-with-spl.imx make target

This image combines the SPL with the i.MX header and U-Boot. This is a
convenient way of having a single image to program on some boot devices.

The i.MX header has to be added to the SPL before appending U-Boot, so that the
boot ROM loads only the SPL.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
diff --git a/.gitignore b/.gitignore
index bff721e..e42d837 100644
--- a/.gitignore
+++ b/.gitignore
@@ -30,6 +30,7 @@
 /u-boot
 /u-boot.hex
 /u-boot.imx
+/u-boot-with-spl.imx
 /u-boot.map
 /u-boot.srec
 /u-boot.ldr