Reimplement udmabuf to FreeBSD

This project aims to implement the udmabuf (User DMA Buffer) driver on FreeBSD, a crucial mechanism for zero-copy memory sharing between userspace applications and kernel subsystems. The absence of udmabuf currently limits FreeBSD's capability to efficiently support modern graphics and virtualization stacks, particularly preventing tools like QEMU from utilizing virtio-gpu with blob resources. The proposed solution involves developing a loadable kernel module that acts as a dma_buf exporter, deeply integrating with FreeBSD's virtual memory subsystem and extending the linuxkpi compatibility layer. Key deliverables include a fully functional udmabuf module implementing the complete set of dma_buf_ops, necessary linuxkpi API extensions for DRM compatibility, end-to-end integration patches for QEMU, and comprehensive ATF test cases accompanied by thorough documentation.