[PATCH] tools: ensure zeroed padding in external FIT images

[Roman Azarenko]

Hello Marek,

On Wed, 2023-08-23 at 20:06 +0200, Marek Vasut wrote:
> Can we use memset and zero out the trailing part of the buffer instead
> ?

That is what I started with, but at the time the ftruncate() approach
seemed simpler.

Now that you suggested memset yourself, I took a stab at it again. I
think I got to the point where I'm happy with the logic, and will submit
v2 tomorrow to give some more time if anyone else has more comments on
v1.

Thank you!