i386: Use DEV_HYPERV to enable HyperV APIC vector

This avoids requiring both 'device hyperv' and 'options HYPERV' for
kernel configs. Instead, just 'device hyperv' can now be used
matching the kernel configuration used for amd64.

Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D44783

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

sys: use .S for assembly language files that use the preprocessor

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/609
Differential Revision: https://reviews.freebsd.org/D35908