bpf, test: add couple of test cases

Add couple of test cases for interpreter but also JITs, f.e. to test that
when imm32 moves are being done, upper 32bits of the regs are being zero
extended.

Without JIT:

  [...]
  [ 1114.129301] test_bpf: #43 MOV REG64 jited:0 128 PASS
  [ 1114.130626] test_bpf: #44 MOV REG32 jited:0 139 PASS
  [ 1114.132055] test_bpf: #45 LD IMM64 jited:0 124 PASS
  [...]

With JIT (generated code can as usual be nicely verified with the help of
bpf_jit_disasm tool):

  [...]
  [ 1062.726782] test_bpf: #43 MOV REG64 jited:1 6 PASS
  [ 1062.726890] test_bpf: #44 MOV REG32 jited:1 6 PASS
  [ 1062.726993] test_bpf: #45 LD IMM64 jited:1 6 PASS
  [...]

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>