Always enable the virtual timer for userspace

We always have it, some languages assume it's present, e.g. go
before 1.20. Enable it by default on arm and arm64.

PR: 269070
Reviewed by: kevans
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D39059

(cherry picked from commit 93d574ea957decec1c95dea9bfa8bc72457cc60d)