ahci: display all AHCI 1.3 HBA capability flags (v2)

Update the AHCI driver to display all of the HBA capabilities defined in the
AHCI 1.3 specification. Some of these are in a new CAP2 (HBA Capabilities
Extended) register which is only defined on AHCI 1.2 or later. The spec says
that undefined registers should always return 0 on read, but to be safe we
assume a value of 0 unless the controller reports AHCI version 1.2 or later.
The value can also be retrieved through sysfs as with the existing capability
field.

For example, on an Intel Ibex Peak (PCH) controller:

ahci 0000:00:1f.2: flags: 64bit ncq sntf stag pm led clo pmp pio slum part ems
sxs apst

We don't do anything special with the new flags yet.

Also, change the code that displays the flags to use the same bit enumerations
that are used to control actual operation.

Signed-off-by: Robert Hancock <hancockrwd@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>