goldfish-opengl: versioning via DRM_IOCTL_VIRTGPU_GET_CAPS

virtio-gpu offers the GET_CAPS hypercall for determining the
capabilities of the host.  Currently, the implementation uses
rcGetHostExtensionsString(..) via the renderControlDecoder.  For
Vulkan and HWC functions, it actually just checks const features
rather than any native rendering library.

Thus, we can keep around rcGetHostExtensionsString(..) until we
nuke GLES, and for future APIs we can use virtgpu functions.

TEST=verify GET_CAPS works with corresponding crosvm changes

Change-Id: I542060a7f665445fbf21416a7ea8c7eb53abe44f
3 files changed