selftests/bpf: Verify zero-extension behavior in load-acquire tests

Verify that 8-, 16- and 32-bit load-acquires are zero-extending by using
immediate values with their highest bit set.  Do the same for the 64-bit
variant to keep the style consistent.

Acked-by: Björn Töpel <bjorn@kernel.org>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com> # QEMU/RVA23
Signed-off-by: Peilin Ye <yepeilin@google.com>
Link: https://lore.kernel.org/r/11097fd515f10308b3941469ee4c86cb8872db3f.1746588351.git.yepeilin@google.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>