gpu: nova-core: add ImemNonSecure section infrastructure

gpu: nova-core: add ImemNonSecure section infrastructure

The GSP booter firmware in Turing and GA100 includes a third memory
section called ImemNonSecure, which is non-secure IMEM.  This section
must be loaded separately from DMEM and secure IMEM, but only if it
actually exists.

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260122222848.2555890-3-ttabi@nvidia.com
[acourbot@nvidia.com: add `debug_assert`.]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>