armv8: fsl: move ccn504 code into FSL Makefile

The generic ARMv8 assembly code contains routines for setting up
a CCN interconnect, though the Freescale SoCs are the only user.
Link this code only for Freescale targets, this saves some precious
bytes in the chronically tight SPL.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>