cpsw: add driver for cpsw ethernet device

CPSW is an on-chip ethernet switch that is found on various SoCs from Texas
Instruments.  This patch adds a simple driver (based on the Linux driver) for
this hardware module.

This patch also adds support to clean and flush dcache during packet send
and receive.

Changes by Sandhya: Added support to clean and flush dcache during packet
		    send/receive and added timeouts.

Signed-off-by: Cyril Chemparathy <cyril@ti.com>
Signed-off-by: Chandan Nath <chandan.nath@ti.com>
Signed-off-by: Satyanarayana, Sandhya <sandhya.satyanarayana@ti.com>
[Ilya: Cleaned cache handling, some style cleanup, some small
fixes, use of internal RAM for descriptors]
Signed-off-by: Ilya Yanok <ilya.yanok@cogentembedded.com>