pci: Make PCIe Eject timeout configurable

[cperciva]

Summary

PCIe mandates a 5 second delay between when the "Attention Button" is
pressed and when the associated device is detached; this is to allow
for the button to be pressed a second time to cancel the ejection. On
some systems this 5 second delay may not be desireable; so introduce a
hw.pci.pcie_hp_detach_timeout sysctl (which can also be set as a loader
tunable) which specifies the timeout in milliseconds (default 5000).
If set to zero, the device is detached immediately.

MFC after: 2 weeks
Sponsored by: Amazon

[cperciva]

Requires https://reviews.freebsd.org/D49584 to work properly (otherwise setting the sysctl(8) gets confused).

[jhb]

sys/dev/pci/pci_pci.c

798

Humm, if I had been more forward-thinking there should be a hw.pci.pcie_hp node and this should be an enable node under that.

802

1076–1086

[cperciva]

Thanks, committed with the two minor changes you suggested.