ata: ahci: mvebu: do Armada 38x configuration only on relevant SoCs

At the beginning, only Armada 38x SoCs where supported by the
ahci_mvebu.c driver. Commit 15d3ce7b ("ata: ahci_mvebu: add
support for Armada 3700 variant") introduced Armada 3700 support. As
opposed to Armada 38x SoCs, the 3700 variants do not have to configure
mbus and the regret option. This patch took care of avoiding such
configuration when not needed in the probe function, but failed to do
the same in the resume path. While doing so looks harmless by
experience, let's clean the driver logic and avoid doing this useless
configuration with Armada 3700 SoCs.

Because the logic is very similar between these two places, it has
been decided to factorize this code and put it in a "Armada 38x
configuration function". This function is part of a new
(per-compatible) platform data structure, so that the addition of such
configuration function for Armada 3700 will be eased.

Fixes: 15d3ce7b

 ("ata: ahci_mvebu: add support for Armada 3700 variant")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>