ahci: increase timout

For some devices, like Marvell 88SE9230, it takes more time
to connect to the device. This patch introduces a special flag
that extends the timeout from around 100ms to around 500ms.

This change is based on the work of: Peter Eriksson <pen@lysator.liu.se>

PR: 243401
Reviewed by: imp
Tested by: dch
MFC after: 3 days
Sponsored by: Equinix
Sponsored by: SkunkWerks, GmbH
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D38413