selftests/bpf: verifier/unpriv converted to inline assembly

Test verifier/unpriv semi-automatically converted to use inline assembly.

The verifier/unpriv.c had to be split in two parts:
- the bulk of the tests is in the progs/verifier_unpriv.c;
- the single test that needs `struct bpf_perf_event_data`
definition is in the progs/verifier_unpriv_perf.c.

The tests above can't be in a single file because:
- first requires inclusion of the filter.h header
(to get access to BPF_ST_MEM macro, inline assembler does
not support this isntruction);
- the second requires vmlinux.h, which contains definitions
conflicting with filter.h.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230421174234.2391278-23-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>