ARM: dts: armada-xp: add label to sdram-controller node

Add the label "sdramc" to the sdram-controller nodes for the Armada-XP
and 98dx3236 SoCs.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>