nfp: bpf: add signed jump insns

This patch adds signed jump instructions (jsgt, jsge, jslt, jsle)
to the nfp jit. As well as adding the additional required raw
assembler branch mask to nfp_asm.h

Signed-off-by: Nic Viljoen <nick.viljoen@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>