arm32, bpf: add support for unconditional bswap instruction

The cpuv4 added a new unconditional bswap instruction with following
behaviour:

BPF_ALU64 | BPF_TO_LE | BPF_END with imm = 16/32/64 means:
dst = bswap16(dst)
dst = bswap32(dst)
dst = bswap64(dst)

As we already support converting to big-endian from little-endian we can
use the same for unconditional bswap. just treat the unconditional scenario
the same as big-endian conversion.
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20230907230550.1417590-5-puranjay12@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

arch/arm/net/bpf_jit_32.c

@@ -1635,10 +1635,12 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 		break;
 	/* dst = htole(dst) */
 	/* dst = htobe(dst) */
-	case BPF_ALU | BPF_END | BPF_FROM_LE:
-	case BPF_ALU | BPF_END | BPF_FROM_BE:
+	case BPF_ALU | BPF_END | BPF_FROM_LE: /* also BPF_TO_LE */
+	case BPF_ALU | BPF_END | BPF_FROM_BE: /* also BPF_TO_BE */
+	/* dst = bswap(dst) */
+	case BPF_ALU64 | BPF_END | BPF_FROM_LE: /* also BPF_TO_LE */
 		rd = arm_bpf_get_reg64(dst, tmp, ctx);
-		if (BPF_SRC(code) == BPF_FROM_LE)
+		if (BPF_SRC(code) == BPF_FROM_LE && BPF_CLASS(code) != BPF_ALU64)
 			goto emit_bswap_uxt;
 		switch (imm) {
 		case 16: