gpu: nova-core: add Chipset::name() method

There are a few cases where we need the lowercase name of a given
chipset, notably to resolve firmware files paths for dynamic loading or
to build the module information.

So far, we relied on a static `NAMES` array for the latter, and some
CString hackery for the former.

Replace both with a new `name` const method that returns the lowercase
name of a chipset instance. We can generate it using the `paste!` macro.

Using this method removes the need to create a `CString` when loading
firmware, and lets us remove a couple of utility functions that now have
no user.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250913-nova_firmware-v6-3-9007079548b0@nvidia.com


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