Summary:
The files in `port/`, such as `port_posix.h`, are layering over the system libraries, so shouldn't include the DB-specific files like `options.h`. This PR remove this dependency.

# How
The reason that `port_posix.h` (or `port_win.h`) include `options.h` is to use `CpuPriority`, as there is a method `SetCpuPriority()` in `port_posix.h` that uses `CpuPriority.`
- I think `SetCpuPriority()` make sense to exist in `port_posix.h` as it provides has platform-dependent implementation
- `CpuPriority` enum is defined in `env.h`, but used in `rocksdb/include` and `port/`.

Hence, let us define `CpuPriority` enum in a common file, say `port_defs.h`, such that both directories `rocksdb/include` and `port/` can include.

When we remove this dependency, some other files have compile errors because they can't find definitions, so add header files to resolve

# Test
make all check -j

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11214

Reviewed By: pdillinger

Differential Revision: D43196910

Pulled By: guowentian

fbshipit-source-id: 70deccb72844cfb08fcc994f76c6ef6df5d55ab9