gpu: nova-core: refactor SEC2 booter loading into BooterFirmware::run()

gpu: nova-core: refactor SEC2 booter loading into BooterFirmware::run()

Move the SEC2 reset/load/boot sequence into a BooterFirmware::run()
method. This is mostly refactoring, with no significant behavior change,
done in preparation for adding an alternative FSP boot path.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260521-nova-unload-v6-4-65f581c812c9@nvidia.com
[acourbot: fix typo in commit message.]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>