kernel crate/module is missing for `linux` feature to work

[zjp-CN]

osl ✗ cargo c --features linux
    Checking osl v0.1.0 (/rust/tmp/repos/osl)
error[E0433]: failed to resolve: use of undeclared crate or module `kernel`
 --> src/linux/error.rs:1:5
  |
1 | use kernel::prelude::*;
  |     ^^^^^^ use of undeclared crate or module `kernel`

error[E0433]: failed to resolve: use of undeclared crate or module `kernel`
 --> src/linux/sleep.rs:1:5
  |
1 | use kernel::delay::usleep_range;
  |     ^^^^^^ use of undeclared crate or module `kernel`

[guoweikang]

Applying OSL on Linux is a slightly complicated task，Refer to https://github.com/guoweikang/i2c-dw-linux-adapter; When enabling the Linux feature, it must be coordinated with other tasks (for example, the project needs to be in the Linux directory)