docs/overview: modify the architecture figure

For dataplane solution architecture figure,
- Remove deliverables.
- Change the colors.
- Add title below the figure.

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

Change-Id: I4150db29b7d3e855996c0c36ad05e4cb2eec4097