rust: device: fix broken intra-doc links

The `pci` module is conditional on CONFIG_PCI. When it's disabled, the
intra-doc link to `pci::Device` causes rustdoc warnings:

warning: unresolved link to `kernel::pci::Device`
   --> rust/kernel/device.rs:163:22
    |
163 | /// [`pci::Device`]: kernel::pci::Device
    |                      ^^^^^^^^^^^^^^^^^^^ no item named `pci` in module `kernel`
    |
    = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

Fix this by making the documentation conditional on CONFIG_PCI.

Fixes: d6e26c1 ("device: rust: expand documentation for Device")
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Dirk Behme <dirk.behme@de.bosch.com>
Link: https://patch.msgid.link/20251231045728.1912024-2-fujita.tomonori@gmail.com
[ Keep the "such as" part indicating a list of examples; fix typos in
  commit message. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: fujita

rust/kernel/device.rs

@@ -67,8 +67,9 @@ static_assert!(core::mem::size_of::<bindings::driver_type>() >= core::mem::size_
 ///
 /// # Implementing Bus Devices
 ///
-/// This section provides a guideline to implement bus specific devices, such as [`pci::Device`] or
-/// [`platform::Device`].
+/// This section provides a guideline to implement bus specific devices, such as:
+#[cfg_attr(CONFIG_PCI, doc = "* [`pci::Device`](kernel::pci::Device)")]
+/// * [`platform::Device`]
 ///
 /// A bus specific device should be defined as follows.
 ///
@@ -160,7 +161,6 @@ static_assert!(core::mem::size_of::<bindings::driver_type>() >= core::mem::size_
 ///
 /// [`AlwaysRefCounted`]: kernel::types::AlwaysRefCounted
 /// [`impl_device_context_deref`]: kernel::impl_device_context_deref
-/// [`pci::Device`]: kernel::pci::Device
 /// [`platform::Device`]: kernel::platform::Device
 #[repr(transparent)]
 pub struct Device<Ctx: DeviceContext = Normal>(Opaque<bindings::device>, PhantomData<Ctx>);