gpu: nova-core: firmware: add support for common firmware header

Several firmware files loaded from userspace feature a common header
that describes their payload. Add basic support for it so subsequent
patches can leverage it.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250913-nova_firmware-v6-5-9007079548b0@nvidia.com


Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>