selftests/bpf: Fix tests to use arch-dependent syscall entry points

Some of the tests are using x86_64 ABI-specific syscall entry points
(such as __x64_sys_nanosleep and __x64_sys_getpgid). Update them to use
architecture-dependent syscall entry names.

Also update fexit_sleep test to not use BPF_PROG() so that it is clear
that the syscall parameters aren't being accessed in the bpf prog.

Note that none of the bpf progs in these tests are actually accessing
any of the syscall parameters. The only exception is perfbuf_bench, which
passes on the bpf prog context into bpf_perf_event_output() as a pointer
to pt_regs, but that looks to be mostly ignored.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/e35f7051f03e269b623a68b139d8ed131325f7b7.1643973917.git.naveen.n.rao@linux.vnet.ibm.com

selftests/bpf: Add trace_vprintk test prog

This commit adds a test prog for vprintk which confirms that:
* bpf_trace_vprintk is writing to /sys/kernel/debug/tracing/trace_pipe
* __bpf_vprintk macro works as expected
* >3 args are printed
* bpf_printk w/ 0 format args compiles
* bpf_trace_vprintk call w/ a fmt specifier but NULL fmt data fails

Approach and code are borrowed from trace_printk test.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210917182911.2426606-9-davemarchevsky@fb.com