android: A few patches towards d3d12 support for Windows Subsystem for Android

For WSA, we want to use Mesa's EGL/GLES stack on top of our d3d12 paravirtualization infrastructure. This requires !13054 (merged), !12268 (merged), !12722 (merged), !13533 (closed), and this series.

Like in WSL, we're currently abusing swrast to be able to initialize without having any DRM devices, except Mesa's Android support only supports kms_swrast, so we have VGEM. I added an option so we turn on EGL_FORCE_RENDERNODE at the board-level without having to make changes in this repo, since we're not using VGEM's dumb buffer ioctls. And we're only including swrast as a gallium driver so that the initialization path lights up and works, but we're not actually rendering with softpipe/llvmpipe. For simplicity and binary size, we don't need to pull in an LLVM dependency, so we want to allow including swrast without llvm, i.e. softpipe.