mrp: Add some missing protobuf definitions

[codecov[bot]]

Codecov Report

Patch coverage: 58.62% and project coverage change: -0.03% :warning:

Comparison is base (b91dfae) 88.67% compared to head (b4c8565) 88.64%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2119 +/- ## ========================================== - Coverage 88.67% 88.64% -0.03% ========================================== Files 162 163 +1 Lines 10973 10991 +18 ========================================== + Hits 9730 9743 +13 - Misses 1243 1248 +5 ``` | [Files Changed](https://app.codecov.io/gh/postlund/pyatv/pull/2119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl) | Coverage Δ | | |---|---|---| | [pyatv/protocols/mrp/protobuf/Origin\_pb2.py](https://app.codecov.io/gh/postlund/pyatv/pull/2119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl#diff-cHlhdHYvcHJvdG9jb2xzL21ycC9wcm90b2J1Zi9PcmlnaW5fcGIyLnB5) | `70.58% <25.00%> (ø)` | | | [...cols/mrp/protobuf/UpdateOutputDeviceMessage\_pb2.py](https://app.codecov.io/gh/postlund/pyatv/pull/2119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl#diff-cHlhdHYvcHJvdG9jb2xzL21ycC9wcm90b2J1Zi9VcGRhdGVPdXRwdXREZXZpY2VNZXNzYWdlX3BiMi5weQ==) | `61.90% <25.00%> (ø)` | | | [...atv/protocols/mrp/protobuf/NowPlayingPlayer\_pb2.py](https://app.codecov.io/gh/postlund/pyatv/pull/2119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl#diff-cHlhdHYvcHJvdG9jb2xzL21ycC9wcm90b2J1Zi9Ob3dQbGF5aW5nUGxheWVyX3BiMi5weQ==) | `78.57% <33.33%> (ø)` | | | [...atv/protocols/mrp/protobuf/UpdatePlayerPath\_pb2.py](https://app.codecov.io/gh/postlund/pyatv/pull/2119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl#diff-cHlhdHYvcHJvdG9jb2xzL21ycC9wcm90b2J1Zi9VcGRhdGVQbGF5ZXJQYXRoX3BiMi5weQ==) | `76.47% <76.47%> (ø)` | | | [pyatv/protocols/mrp/protobuf/\_\_init\_\_.py](https://app.codecov.io/gh/postlund/pyatv/pull/2119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl#diff-cHlhdHYvcHJvdG9jb2xzL21ycC9wcm90b2J1Zi9fX2luaXRfXy5weQ==) | `99.57% <100.00%> (+<0.01%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/postlund/pyatv/pull/2119/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl)

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