rust: macros: take string literals in module!

Instead of taking binary string literals, take string ones instead,
making it easier for users to define a module, i.e. instead of
calling `module!` like:

    module! {
        ...
        name: b"rust_minimal",
        ...
    }

now it is called as:

    module! {
        ...
        name: "rust_minimal",
        ...
    }

Module names, aliases and license strings are restricted to
ASCII only. However, the author and the description allows UTF-8.

For simplicity (avoid parsing), escape sequences and raw string
literals are not yet handled.

Link: https://github.com/Rust-for-Linux/linux/issues/252
Link: https://lore.kernel.org/lkml/YukvvPOOu8uZl7+n@yadro.com/
Signed-off-by: Gary Guo <gary@garyguo.net>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/macros/lib.rs

@@ -25,20 +25,20 @@ use proc_macro::TokenStream;
 ///
 /// module!{
 ///     type: MyModule,
-///     name: b"my_kernel_module",
-///     author: b"Rust for Linux Contributors",
-///     description: b"My very own kernel module!",
-///     license: b"GPL",
+///     name: "my_kernel_module",
+///     author: "Rust for Linux Contributors",
+///     description: "My very own kernel module!",
+///     license: "GPL",
 ///     params: {
 ///        my_i32: i32 {
 ///            default: 42,
 ///            permissions: 0o000,
-///            description: b"Example of i32",
+///            description: "Example of i32",
 ///        },
 ///        writeable_i32: i32 {
 ///            default: 42,
 ///            permissions: 0o644,
-///            description: b"Example of i32",
+///            description: "Example of i32",
 ///        },
 ///    },
 /// }