Part of implementing #9904

This task is a smaller alternative to #9980. It is a MUST because we must either complete this task or #9980

Move fuzz_privkey.c and fuzz_pubkey.c to the TF-PSA-Crypto repository. This enables us to keep these programs even though they still use the legacy API without rewriting them fully for the PSA API.

This task is done when programs/fuzz/fuzz_privkey.c and programs/fuzz/fuzz_pubkey.c reside in the TF-PSA-Crypto repo and can be built and run from there.