This patch extends the FIP tool to include the certificates
generated by the 'cert_create' tool.

If GENERATE_COT build option is enabled, the Makefile adds the
certificates as dependencies to create the FIP file. Thus, make
target 'fip' will also build the certificates as part of the
Trusted Firmware build process.

Change-Id: I5eee500da7f7be6cfb6e3df0423599739d260074