ci: Run clippy for each specific feature

The build is run against "--all-features", "pci,acpi", "pci" and "mmio"
separately. The clippy validation must be run against the same set of
features in order to validate the code is correct.

Because of these new checks, this commit includes multiple fixes
related to the errors generated when manually running the checks.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/vm.rs

@@ -695,7 +695,6 @@ mod tests {
                 assert!(state.valid_transition(VmState::Shutdown).is_ok());
                 assert!(state.valid_transition(VmState::Paused).is_err());
             }
-            _ => {}
         }
     }