media: atmel: atmel-isc: add DMA to register offsets

The DMA submodule is a part of the atmel-isc pipeline, and stands for
Direct Memory Access. It acts like a master on the AXI bus of the SoC, and
can directly write the RAM area with the pixel data from the ISC internal
sram.
Add dma to the reg offsets struct.
This will allow different products to have a different reg offset for this
particular module.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>