gpu: nova-core: firmware: process and prepare the GSP firmware

The GSP firmware is a binary blob that is verified, loaded, and run by
the GSP bootloader. Its presentation is a bit peculiar as the GSP
bootloader expects to be given a DMA address to a 3-levels page table
mapping the GSP firmware at address 0 of its own address space.

Prepare such a structure containing the DMA-mapped firmware as well as
the DMA-mapped page tables, and a way to obtain the DMA handle of the
level 0 page table.

Then, move the GSP firmware instance from the `Firmware` struct to the
`start_gsp` method since it doesn't need to be kept after the GSP is
booted.

As we are performing the required ELF section parsing and radix3 page
table building, remove these items from the TODO file.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250913-nova_firmware-v6-7-9007079548b0@nvidia.com


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