There's a merged pull request on the void-packages repository

mesa: add Broadcom vulkan driver
https://github.com/void-linux/void-packages/pull/34778

Description:
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#### Testing the changes
- I tested the changes in this PR: **briefly**

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#### Local build testing
- I built this PR locally for my native architecture, aarch64

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I created a new subpackage to build vulkan drivers for the Raspberry Pi 4. They seem to be working correctly, given the output of `vulkaninfo` from `Vulkan-Tools`, but I haven't actually tested any graphical workload, since `vkcube` is missing from `Vulkan-Tools` in `aarch64`.

P.S. -- I removed the update to 21.3.3 to keep this PR more feature isolated.