rust: drm: Drop the use of Opaque for ioctl arguments

rust: drm: Drop the use of Opaque for ioctl arguments

With the Opaque<T>, the expectations are that Rust should not
make any assumptions on the layout or invariants of the wrapped
C types. That runs rather counter to ioctl arguments, which must
adhere to certain data-layout constraints. By using Opaque<T>,
ioctl handlers are forced to use unsafe code where none is actually
needed. This adds needless complexity and maintenance overhead,
brining no safety benefits.
Drop the use of Opaque for ioctl arguments as that is not the best
fit here.

Signed-off-by: Beata Michalska <beata.michalska@arm.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250626162313.2755584-1-beata.michalska@arm.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>