drm/tyr: use shmem GEM object type in TyrDrmDriver

drm/tyr: use shmem GEM object type in TyrDrmDriver

Tyr buffer objects are shmem-backed, so the driver should use
drm::gem::shmem::Object<BoData> as its GEM object type instead of the base
drm::gem::Object<BoData> type.

Switching to the shmem GEM object type matches how Tyr allocates and
manages its buffer objects, and uses the shmem-specific GEM abstraction
provided by the DRM Rust bindings.

Select RUST_DRM_GEM_SHMEM_HELPER to ensure the required helpers are
available when DRM_TYR is enabled.

Signed-off-by: Alvin Sun <alvin.sun@linux.dev>
Signed-off-by: Deborah Brouwer <deborah.brouwer@collabora.com>
Link: https://patch.msgid.link/20260428-fw-boot-prerequisites-v1-3-c69af9abe1af@collabora.com
Signed-off-by: Alice Ryhl <aliceryhl@google.com>