nfp: bpf: fix ALU32 high bits clearance bug

NFP BPF JIT compiler is doing a couple of small optimizations when jitting
ALU imm instructions, some of these optimizations could save code-gen, for
example:

  A & -1 =  A
  A |  0 =  A
  A ^  0 =  A

However, for ALU32, high 32-bit of the 64-bit register should still be
cleared according to ISA semantics.

Fixes: cd7df56e

 ("nfp: add BPF to NFP code translator")
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>