OMAP5 contains a single DES crypto accelerator instance. Add node for
this in DT to enable it.

We keep the node disabled for now, as it appears OMAP5 platform is
running out of available DMA channels, and DES is the least interesting
crypto accelerator available on the device.
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>