ahci: provide sunxi SATA driver using AHCI platform framework

ahci: provide sunxi SATA driver using AHCI platform framework

This enables the necessary clocks, in AHB0 and in PLL6_CFG. This is done
for sun7i only since I don't have access to any other sunxi platforms
with sata included.

The PHY setup is derived from the Alwinner releases and Linux, but is mostly
undocumented.

The Allwinner AHCI controller also requires some magic (and, again,
undocumented) DMA initialisation when starting a port.  This is added under a
suitable ifdef.

This option is enabled for Cubieboard, Cubieboard2 and Cubietruck based on
contents of Linux DTS files, including SATA power pin config taken from the
DTS. All build tested, but runtime tested on Cubieboard2 and Cubietruck only.

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>