Revert "Platform: CS315: Add CC3xx support"

This reverts commit 4ccf459c.
This reverts commit a3cbd5d3.

Reason: The CryptoCell support will not be needed in Corstone-315 so
removed the files to avoid confusion.

Change-Id: I2b63a8b582723c466efcb4ffc361e47d3bd37590
Signed-off-by: Bence Balogh <bence.balogh@arm.com>