[rom_ext] Migrate to ECDSA verification of application firmware

[cfrantz]

Migrate to ECDSA verification of application firmware.

Currently, the ROM_EXT uses RSA3K keys to validate application firmware, but we want to use ECDSA verification instead and eliminate the use of RSA keys.

• [ ] Migrate the ES ROM_EXT to using ECDSA keys
  • [x] Cherry-pick ECDSA changes from master branch.
  • [x] Integrate ECDSA sigverify into the ROM_EXT.
  • [ ] Change FPGA application keys to ECDSA keys.
  • [ ] Change SiVAL application keys to ECDSA keys.
  • [ ] Change ProdA application keys to ECDSA keys.
  • [ ] Change ProdC application keys to ECDSA keys.
• [ ] Eliminate RSA application keys from the earlgrey_es_sival branch.
• [ ] Cherry-pick the ROM_EXT changes and new keys to master
• [ ] Cherry-pick the ROM_EXT changes and new keys to earlgrey_1.0.0

[cfrantz]

#24544 #24643