gpu: nova-core: convert PFB registers to kernel register macro

gpu: nova-core: convert PFB registers to kernel register macro

Convert all PFB registers to use the kernel's register macro and update
the code accordingly.

NV_PGSP_QUEUE_HEAD was somehow caught in the PFB section, so move it to
its own section and convert it as well.

Reviewed-by: Eliot Courtney <ecourtney@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260325-b4-nova-register-v4-4-bdf172f0f6ca@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>