el3_payload: Add initial platform support for RD-N1-Edge

RD-N1-Edge platform consists of two clusters of four CPUs
each. CPU0 of the first cluster is the primary CPU. SoC UART0 is
used for the console log.

Change-Id: I724c772f95d590154536e7bc1544976e55b983cf
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>
3 files changed