dt-bindings: marvell: Document the AC5/AC5X compatibles

Describe the compatible properties for the Marvell Alleycat5/5X switches
with integrated CPUs.

Alleycat5:
* 98DX2538: 24x1G + 2x10G + 2x10G Stack
* 98DX2535: 24x1G + 4x1G Stack
* 98DX2532: 8x1G + 2x10G + 2x1G Stack
* 98DX2531: 8x1G + 4x1G Stack
* 98DX2528: 24x1G + 2x10G + 2x10G Stack
* 98DX2525: 24x1G + 4x1G Stack
* 98DX2522: 8x1G + 2x10G + 2x1G Stack
* 98DX2521: 8x1G + 4x1G Stack
* 98DX2518: 24x1G + 2x10G + 2x10G Stack
* 98DX2515: 24x1G + 4x1G Stack
* 98DX2512: 8x1G + 2x10G + 2x1G Stack
* 98DX2511: 8x1G + 4x1G Stack

Alleycat5X:
* 98DX3500: 24x1G + 6x25G
* 98DX3501: 16x1G + 6x10G
* 98DX3510: 48x1G + 6x25G
* 98DX3520: 24x2.5G + 6x25G
* 98DX3530: 48x2.5G + 6x25G
* 98DX3540: 12x5G/6x10G + 6x25G
* 98DX3550: 24x5G/12x10G + 6x25G

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Vadym Kochan <vadym.kochan@plvision.eu>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>