iommu/omap: Add devicetree support

As OMAP2+ is moving to a full DT boot for all SoC families, commit
7ce93f31 "ARM: OMAP2+: Fix more missing data for omap3.dtsi file"
adds basic DT bits for OMAP3. But the driver is not yet converted,
so this will not work and driver will not be probed. Convert it!

The legacy boot mode is still supported until OMAP3 is converted
to DT-boot only.

Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
[s-anna@ti.com: dev_name adaptation and improved error checking]
Signed-off-by: Suman Anna <s-anna@ti.com>
[tony@atomide.com: Ack for arch/arm/*omap* parts]
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>