设备驱动模型：完善platform bus相关内容。并注册串口到sysfs (#403)

* 完成初始化platform bus
* 删除旧的sysfs
* 把uart驱动移动到tty/serial文件夹下
* 完成将串口挂载到sysfs
* 修复vfs系统调用未能follow symlink的问题
* 修复shell未能正确获取pwd的问题

kernel/src/driver/tty/tty_driver.rs

@@ -0,0 +1,61 @@
+use core::fmt::Debug;
+
+use alloc::sync::Arc;
+
+use crate::driver::base::device::driver::Driver;
+
+use super::tty_device::TtyDevice;
+
+/// TTY 驱动
+///
+///
+/// 参考 https://opengrok.ringotek.cn/xref/linux-6.1.9/include/linux/tty_driver.h#434
+pub trait TtyDriver: Debug + Send + Sync + Driver {
+    fn driver_name(&self) -> &str;
+    fn dev_name(&self) -> &str;
+
+    fn metadata(&self) -> &TtyDriverMetadata;
+
+    fn other(&self) -> Option<&Arc<dyn TtyDriver>>;
+
+    fn ttys(&self) -> &[Arc<TtyDevice>];
+
+    fn tty_ops(&self) -> Option<&'static dyn TtyDriverOperations> {
+        None
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+#[allow(dead_code)]
+pub struct TtyDriverMetadata {
+    ///  name of the driver used in /proc/tty
+    driver_name: &'static str,
+    /// used for constructing /dev node name
+    dev_name: &'static str,
+    /// used as a number base for constructing /dev node name
+    name_base: i32,
+    /// major /dev device number (zero for autoassignment)
+    major: i32,
+    /// the first minor /dev device number
+    minor_start: i32,
+    drv_type: TtyDriverType,
+    subtype: TtyDriverSubtype,
+}
+
+/// https://opengrok.ringotek.cn/xref/linux-6.1.9/include/linux/tty_driver.h#411
+#[derive(Debug, Clone, Copy)]
+pub enum TtyDriverType {}
+
+/// https://opengrok.ringotek.cn/xref/linux-6.1.9/include/linux/tty_driver.h#412
+#[derive(Debug, Clone, Copy)]
+pub enum TtyDriverSubtype {}
+
+bitflags! {
+    /// https://opengrok.ringotek.cn/xref/linux-6.1.9/include/linux/tty_driver.h?fi=SERIAL_TYPE_NORMAL#492
+    pub struct TtyDriverFlags: u64 {
+
+    }
+}
+
+/// 参考 https://opengrok.ringotek.cn/xref/linux-6.1.9/include/linux/tty_driver.h#350
+pub trait TtyDriverOperations {}