CCI: Adapt for specific product at run time

CCI: Adapt for specific product at run time

The current build system and driver requires the CCI product to be
specified at build time. The device constraints can be determined at run
time from its ID registers, obviating the need for specifying them
ahead.

This patch adds changes to identify and validate CCI at run time. Some
global variables are renamed to be in line with the rest of the code
base.

The build option ARM_CCI_PRODUCT_ID is now removed, and user guide is
updated.

Change-Id: Ibb765e349d3bc95ff3eb9a64bde1207ab710a93d
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>