ARM: tegra: enable DFU for RAM

This allows transferring data directly to/from RAM. For example, one
could create a boot script that starts DFU on a RAM region, then once
DFU exits (which is under the control of the attached USB host, via a
USB bus reset), uses the code/data that was received over DFU.

Signed-off-by: Stephen Warren <swarren@nvidia.com>