Documentation: gpu: nova-core: Document vbios layout

Add detailed explanation and block diagrams of the layout of the vBIOS
on Nvidia GPUs. This is important to understand how nova-core boots an
Nvidia GPU.

[ Applied Timur Tabi's feedback on providing link to BIT documentation. ]

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250708-nova-docs-v4-5-9d188772c4c7@nvidia.com


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