Use sel4-config crate plus minor fixes
- Use sel4-config crate, call it in build.rs, and import generated sel4-config.rs in lib.rs
- Remove explicit feature flags for sel4 config in Cargo.toml
- Change feature flags used to match sel4 config
- Add missing conditional compilation feature flags
- Add missing VTX type aliases to seL4_CPtr
- Add missing VTX struct seL4_VCPUContext
- Fix seL4_BenchmarkGetThreadUtilization syscall stub
Waiting on sel4-config!2 (merged)