Leave hypervisor mode upon startup on ARMv7

If ARMv7 boots in HYP mode, switch to SVC32.

Reviewed by: ian
Submitted by: Wojciech Macek <wma@semihalf.com>

Jakub Palider  <jpa@semihalf.com>

Obtained from: Semihalf
Sponsored by: Annapurna Labs
Differential Revision: https://reviews.freebsd.org/D1810