Changes to 'tools/cert_create' folder, to include platform defined
certificates, keys, and extensions.

NXP SoC lx2160a : based platforms requires additional
FIP DDR to be loaded before initializing the DDR.

To enable chain of trust on these platforms, FIP DDR
image needs to be authenticated, additionally.

Platform specific folder 'tools/nxp/cert_create_helper'
is added to support platform specific macros and definitions.
Signed-off-by: Pankaj Gupta <pankaj.gupta@nxp.com>
Change-Id: I4752a30a9ff3aa1d403e9babe3a07ba0e6b2bf8f