omap iommu: renamed omap3-iommu to omap-iommu

This patch includes changes to omap3-iommu.c file to make it generic
for all OMAPs. Renamed omap3-iommu.c to omap-iommu.c

[Hiroshi DOYU: Remove unnecessary "iommu-y" in Makefile]

Signed-off-by: Hari Kanigeri <h-kanigeri2@ti.com>
Signed-off-by: Hiroshi DOYU <Hiroshi.DOYU@nokia.com>