MFC r340129, r340195, r340198

r340129:
capsicum: allow ppoll(2) in capability mode

We already allow to use poll(2). There is no reason to disallow
ppoll(2).

PR: 232495
Submitted by: Stefan Grundmann <sg2342@googlemail.com>
Reviewed by: cem, oshogbo

r340195:
capsicum: Add ppoll and freebsd32_ppoll to compat32.

PR: 232495
Pointed out by: brooks

r340198:
Remove ppoll. freebsd32 doesn't define a ppoll syscall.

Reported by: jhb