ARM: OMAP2+: Move iopgtable header to drivers/iommu/

The iopgtable header file is only used by the iommu & iovmm drivers, so
move it to drivers/iommu/, as part of the single zImage effort.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Omar Ramirez Luna <omar.luna@linaro.org>
Signed-off-by: Ido Yariv <ido@wizery.com>
Acked-by: Ohad Ben-Cohen <ohad@wizery.com>
Acked-by: Joerg Roedel <joro@8bytes.org>
[tony@atomide.com: updated to be earlier in the series]
Signed-off-by: Tony Lindgren <tony@atomide.com>