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>
diff --git a/plat/arm/css/drivers/scmi/scmi_private.h b/plat/arm/css/drivers/scmi/scmi_private.h
index a4f4179..6530573 100644
--- a/plat/arm/css/drivers/scmi/scmi_private.h
+++ b/plat/arm/css/drivers/scmi/scmi_private.h
@@ -7,6 +7,8 @@
 #ifndef SCMI_PRIVATE_H
 #define SCMI_PRIVATE_H
 
+#include <lib/mmio.h>
+
 /*
  * SCMI power domain management protocol message and response lengths. It is
  * calculated as sum of length in bytes of the message header (4) and payload