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

(cherry picked from commit e045163cce955c32332a02a8eb9a48f3c2cd3c3f)