selftests/bpf: Add verifier tests for better jmp32 register bounds

Three test cases are added.
Test 1: jmp32 'reg op imm'.
Test 2: jmp32 'reg op reg' where dst 'reg' has unknown constant
        and src 'reg' has known constant
Test 3: jmp32 'reg op reg' where dst 'reg' has known constant
        and src 'reg' has unknown constant

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191121170651.449096-1-yhs@fb.com