iommu/omap: Remove duplicate declarations

The omap_iommu_save_ctx() and omap_iommu_restore_ctx() declarations
are defined in include/linux/omap-iommu.h and do not belong in the
internal drivers/iommu/omap-iommu.h header, so remove them.

Signed-off-by: Suman Anna <s-anna@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>