ata: ahci: implement init callback ...

Now that we have framework support for delayed probing of
ata devices implement it in the ahci driver to actually make use
of it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ata: Add ahci support ...

This adds ahci controller support based on U-Boot ahci support. Unlike
U-Boot we do not push the SCSI layer in between, but use the ata interface
directly. Tested on a Freescale i.MX53.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>