llvmpipe,lavapipe: add external memory fd(VK) and memory object fd(GL) extensions
Add capability to import/export external memory via memoryfd file descriptors to/from llvmpipe and lavapipe.
This change enables the following extensions:
- GL_KHR_memory_object
- GL_KHR_memory_object_fd
- VK_EXT_external_memory_fd
Edited by Thomas Wagner