selftests/bpf: test cases for compute_live_registers()

Cover instructions from each kind:
- assignment
- arithmetic
- store/load
- endian conversion
- atomics
- branches, conditional branches, may_goto, calls
- LD_ABS/LD_IND
- address_space_cast

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250304195024.2478889-6-eddyz87@gmail.com


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