Add support for ahci on sysbus. Signed-off-by: Rob Herring <rob.herring@calxeda.com> Signed-off-by: Mark Langsdorf <mark.langsdorf@calxeda.com> Reviewed-by: Andreas Färber <afaerber@suse.de> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>