ahci: make number of ports runtime determined

ahci: make number of ports runtime determined

Different AHCI controllers have a different number of ports, so the core
shouldn't care about the amount of ports available.

This patch makes the number of ports available to the AHCI core runtime
configurable, allowing us to have multiple different AHCI implementations
with different amounts of ports.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 2c4b9d0ea42c27ec2112e437a0fa954afe73bd23)