ARM: dts: imem: Add imem node to kona device tree

Imem is a fast onchip memory used for various debug features and
dma transactions. Add a imem device tree node for kona.

Change-Id: I60fd11cd607312842b2444b77cb6a4c44743f28b
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>