Documentation: dt-bindings: reformat and order list of ahci-platform compatibles

The ahci-platform.txt Device Tree binding documentation is gaining a
growing number of compatible strings, and it will gain one more with
the addition of the Marvell Armada 380 AHCI support. It is therefore
time to reformat this list into a proper bullet list, and more
importantly order it alphabetically;

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Tejun Heo <tj@kernel.org>