riscv, bpf: Add bpf trampoline support for RV64

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. We can't wait to support bpf trampoline on RV64.
The related tests have passed, as well as the test_verifier with no new
failure ceses.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Acked-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/bpf/20230215135205.1411105-5-pulehui@huaweicloud.com