bpf, tests: Add BPF_MOV tests for zero and sign extension

Tests for ALU32 and ALU64 MOV with different sizes of the immediate
value. Depending on the immediate field width of the native CPU
instructions, a JIT may generate code differently depending on the
immediate value. Test that zero or sign extension is performed as
expected. Mainly for JIT testing.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210809091829.810076-3-johan.almbladh@anyfinetworks.com