[U-Boot] make: how to add post-build step?

[V, Aneesh]

Hi, 

We would like to add a post-build step for OMAP4430SDP. The intention of this step is to attach a header at the beginning of u-boot.bin and create a new binary. 

We do not mind having this as part of the main make step(i.e. as part of the target ALL) or as a separate target(let's say "omap4_header"). 

1. Do we need to modify the top-level Makefile for this? OR 
2. Can we do this somehow through the board level config.mk? 

If 2 is not possible, will you take a patch to do this by 1. We can try to make this as generic as possible. Attaching headers may be done by other boards too? 

Has this been done earlier? Any input on this will be appreciated. 

Regards,
Aneesh