ARM: dts: aspeed-romulus: Update Romulus system

 - Fix incorrect RAM size
 - Remove alias; these are now specified in the dtsi
 - Add newly upstreamed devices
 - Include OpenBMC flash layout

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>