Add raspihats switch platform

[florincosta]

Description:

The raspihats switch platform allows you to control the digital outputs of your raspihats boards.

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#2574

Example entry for configuration.yaml (if applicable):

switch:
  - platform: raspihats
    i2c_hats:
      - board: DI6acDQ6rly
        address: 0x60
        channels:
          - index: 0
            name: Fan Office
            invert_logic: true
            initial_state: true
          - index: 1
            name: Light Office

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[fabaff]

Successor of #7639.

[balloob]

Nice 🐬 👍