riscv, bpf: Factor common RISC-V JIT code

This patch factors out code that can be used by both the RV64 and RV32
BPF JITs to a common bpf_jit.h and bpf_jit_core.c.

Move struct definitions and macro-like functions to header. Rename
rv_sb_insn/rv_uj_insn to rv_b_insn/rv_j_insn to match the RISC-V
specification.

Move reusable functions emit_body() and bpf_int_jit_compile() to
bpf_jit_core.c with minor simplifications. Rename emit_insn() and
build_{prologue,epilogue}() to be prefixed with "bpf_jit_" as they are
no longer static.

Rename bpf_jit_comp.c to bpf_jit_comp64.c to be more explicit.

Co-developed-by: Xi Wang <[email protected]>
Signed-off-by: Xi Wang <[email protected]>
Signed-off-by: Luke Nelson <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Reviewed-by: Björn Töpel <[email protected]>
Acked-by: Björn Töpel <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

arch/riscv/net/Makefile

@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
-obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o
+
+obj-$(CONFIG_BPF_JIT) += bpf_jit_core.o bpf_jit_comp64.o