scripts: generate_rust_analyzer.py: reduce cfg plumbing

scripts: generate_rust_analyzer.py: reduce cfg plumbing

Pass `pin_init{,_internal}-cfgs` from rust/Makefile to
scripts/generate_rust_analyzer.py. Remove hardcoded `cfg`s in
scripts/generate_rust_analyzer.py for `pin-init{,-internal}` now that
these are passed from `rust/Makefile`.

Centralize `cfg` lookup in scripts/generate_rust_analyzer.py in
`append_crate` to avoid having to do so for each crate.

Reviewed-by: Jesung Yang <y.j3ms.n@gmail.com>
Acked-by: Benno Lossin <lossin@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://patch.msgid.link/20260127-rust-analyzer-pin-init-duplication-v3-2-118c48c35e88@kernel.org
Signed-off-by: Tamir Duberstein <tamird@kernel.org>