Convert to virtual manifest and add i2c workspace

This converts the Cargo.toml to a virtual manifest, removes the
src/lib.rs file and adds basic workspace for i2c backend device.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Cargo.toml

@@ -1,12 +1,5 @@
-[package]
-name = "crate-template"
-version = "0.1.0"
-authors = ["TODO"]
-description = "This is a template for creating rust-vmm repositories."
-repository = "https://github.com/rust-vmm/crate-template"
-readme = "README.md"
-keywords = ["virt"]
-license = "Apache-2.0 OR BSD-3-Clause"
-edition = "2018"
+[workspace]
 
-[dependencies]
+members = [
+    "src/i2c",
+]