gpu: nova-core: falcon: add distinct base address for PFALCON2

gpu: nova-core: falcon: add distinct base address for PFALCON2

Falcon engines have two distinct register bases: `PFALCON` and
`PFALCON2`. So far we assumed that `PFALCON2` was located at `PFALCON +
0x1000` because that is the case of most engines, but there are
exceptions (NVDEC uses `0x1c00`).

Fix this shortcoming by leveraging the redesigned relative registers
definitions to assign a distinct `PFalcon2Base` base address to each
falcon engine.

Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20250718-nova-regs-v2-16-7b6a762aa1cd@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>