loongarch64: backport kernel BPF trampoline

loongarch64: backport kernel BPF trampoline

Enable xdp-loader to attach multiple XDP programs to a single interface by
backporting the BPF trampoline implementation from Linux kernel 6.17 to
6.12 for LoongArch64.

The xdp-loader utility relies on libxdp, which in turn requires kernel
support for BPF trampoline. While x86_64 and other architectures have
this feature, LoongArch64 only gained it in kernel 6.17. Without this
backport, xdp-loader fails on LoongArch64 systems running kernel 6.12.

Changes backported include:
- BPF trampoline infrastructure for LoongArch64
- Necessary JIT compiler updates
- Related BPF subsystem changes

This allows full compatibility with the xdp-tools ecosystem on LoongArch64
systems running older kernel versions.

Reference: https://github.com/xdp-project/xdp-tools/tree/main/lib/libxdp

Signed-off-by: Vincent Li <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/21077
Signed-off-by: Christian Marangi <[email protected]>