riscv, bpf: Unify 32-bit zero-extension to emit_zextw

For code unification, add emit_zextw wrapper to unify all the 32-bit
zero-extension operations.
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@kernel.org>
Link: https://lore.kernel.org/bpf/20240115131235.2914289-3-pulehui@huaweicloud.com

arch/riscv/net/bpf_jit.h

@@ -1092,6 +1092,12 @@ static inline void emit_sextw(u8 rd, u8 rs, struct rv_jit_context *ctx)
 	emit_addiw(rd, rs, 0, ctx);
 }
 
+static inline void emit_zextw(u8 rd, u8 rs, struct rv_jit_context *ctx)
+{
+	emit_slli(rd, rs, 32, ctx);
+	emit_srli(rd, rd, 32, ctx);
+}
+
 #endif /* __riscv_xlen == 64 */
 
 void bpf_jit_build_prologue(struct rv_jit_context *ctx);