bpf, tests: Add more ALU64 BPF_MUL tests

This patch adds BPF_MUL tests for 64x32 and 64x64 multiply. Mainly
testing 32-bit JITs that implement ALU64 operations with two 32-bit
CPU registers per operand.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210809091829.810076-8-johan.almbladh@anyfinetworks.com