[TF-A] FIP header flags available for feature selection

Hello,

The fip header has reserved fields available for platform specific use. The fiptool allows these header fields to be filled in using the --plat-toc-flags.

A call needs to be available in the ATF framework to get these flags without accessing the FIP file again to get these flags. We have a solution we've used for ATF for quite some time to access these flags.

It's finally being upstreamed here: https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/2839

If there are any other efficient methods to access these flags or a better proposal please suggest.

Thanks, Scott