dt-bindings: marvell: a38x: add solidrun armada 388 clearfog boards

Add DT compatible for SolidRun Armada-388 based Clearfog Base and Pro
boards, which are already in place in-tree.

There are already 3 distinct dts in tree for these *two* boards,
declaring particular compatible strings:
the generic "armada-388-clearfog.dts" is a legacy name for the Pro
version, old versions of u-boot built when only one variant existed
explicitly boot by this name.
The other two add explicit -pro / -base suffix to the filename, these
are preferred and chosen by latest u-boot.

Note that both compatibles and model field include the string "A1".
At least up to revision 2.0 of the board, this had been printed
on the pcb. However in marketing material and conversations it is
usually omitted. "Clearfog Pro" and "Clearfog Pro A1" always mean
exactly the same product.

Technically Base and Pro variants are similar enough that they can
successfully boot with each other's dts. Hence it makes (some)
sense for them to share the "clearfog-a1" compatible.

Add bindings for the explicit variants -pro and -base - including a
shared compatible string between the two.

Signed-off-by: Josua Mayer <josua@solid-run.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>