Add char device to simple file system

[gaotianyu1350]

Add some functions and attributes to INodeImpl and SimpleFileSystem in rcore-fs-sfs to support char device.

[gaotianyu1350]

LGTM. BTW, what's the usage of link_inodeimpl?

link_inodeimpl(device_file_name, inode_impl)

• name: string: name of the device file
• inode_impl: &Arc<INodeImpl>: which represents the device file

eg:

// add device to sfs
SFS.new_device_inode(1, STDIN.clone()) // STDIN is INode implementing stdin
// get a new INodeImpl of a device
let stdin_inodeimpl = SFS.new_inode_chardevice(1) // 1 is the device number
// link it to /dev
dev_inode_impl.link_inodeimpl("stdin", &stdin_inodeimpl) // dev_inode_impl is INodeImpl of "/dev"

[jiegec]

Okay, got it.