Add an ACPI attachement to the ahci_generic driver

[andrew]

Summary

This adds a second attachment to the existing ahci_generic driver
for acpi. This will attach on the AMD Opteron a1100.

[emaste]

sys/dev/ahci/ahci_generic.c

50 ↗

(On Diff #23089)

Minor consistency point, maybe have corresponding DEV_ACPI/FDT blocks for each case in the same order - i.e., headers, probe routines, device_method_t/driver_t

[mav]

I have no objections.