ata: ahci_mvebu: add support for Armada 3700 variant

The main difference in the new Armada 3700 is that no address
decoding needs to take place in the driver probe.

[gregory.clement@free-electrons.com: reformulate the commit log]

Signed-off-by: Lior Amsalem <alior@marvell.com>
Reviewed-by: Nadav Haklai <nadavh@marvell.com>
Tested-by: Nadav Haklai <nadavh@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Tejun Heo <tj@kernel.org>