Enable Capsicum on armv6/armv7

We ought to be consistent across our Tier-1 and nearly-Tier-1
architectures, so enable Capsicum for 32-bit armv6/armv7 by default.

PR: 204008
Reviewed by: ian, oshogbo
Approved by: re (gjb)
Relnotes: Yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D17023