LoongArch: BPF: Add bpf trampoline support for Loongarch

BPF trampoline is the critical infrastructure of the BPF subsystem, acting
as a mediator between kernel functions and BPF programs. Numerous important
features, such as using BPF program for zero overhead kernel introspection,
rely on this key component.

The related tests have passed, Including the following technical points:
1. fentry
2. fmod_ret
3. fexit

The following related testcases passed on LoongArch:
sudo ./test_progs -a fentry_test/fentry
sudo ./test_progs -a fexit_test/fexit
sudo ./test_progs -a fentry_fexit
sudo ./test_progs -a modify_return
sudo ./test_progs -a fexit_sleep
sudo ./test_progs -a test_overhead
sudo ./test_progs -a trampoline_count

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202507100034.wXofj6VX-lkp@intel.com/
Co-developed-by: George Guo <guodongtai@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Tested-by: Vincent Li <vincent.mc.li@gmail.com>
Reviewed-by: Hengqi Chen <hengqi.chen@gmail.com>
Reviewed-by: Huacai Chen <chenhuacai@kernel.org>

Author: Chenghao Duan