o Move options IOMMU from Debugging section back to the Bus section

where it originally was. The bug introduced in r366267.

o Remove options IOMMU from i386/MINIMAL as we don't have it in

i386/GENERIC.

Reported by: Harry Schmalzbauer <freebsd@omnilan.de>
Reviewed by: kib
Sponsored by: Innovate DSbD
Differential Revision: https://reviews.freebsd.org/D27399