ARM: dts: mvebu: Add CRS305-1G-4S board

MikroTik CRS305-1G-4S board has a switch chip with an integrated
Marvell Prestera 98DX3236 CPU.

This commit includes two board variants, namely the factory
default one and a Bit variant. The Bit variant has a
bigger Macronix flash.

This device tree includes basic Linux support.

Signed-off-by: Luka Kovacic <luka.kovacic@sartura.hr>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Jakov Petrina <jakov.petrina@sartura.hr>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>