Documentation: gpu: nova-core: Document basics of the Falcon

Instances of the Falcon microcontroller appear in modern Nvidia GPUs and
are crucial to the GPU boot process. Document some concepts which will
make nova-core boot code easier to digest. All the information is
derived from public sources such as public documents, OpenRM and Nouveau
code.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250708-nova-docs-v4-8-9d188772c4c7@nvidia.com


Signed-off-by: Danilo Krummrich <dakr@kernel.org>