plat/arm/n1sdp: define the uart constants for N1SDP

This patch removes the dependency of the N1SDP on soc
css defines in order to let the N1SDP platform port
define the uart related constants.

Change-Id: If13796f278586a01512ee99615502b30e478189e
Signed-off-by: Deepak Pandey <Deepak.Pandey@arm.com>
4 files changed