pci/n1sdp: Disable HotPlug

Work around an issue when HotPlug is enabled where pcib3 and pcib5
continuously report the following:

pcib3: HotPlug interrupt: 0x30
pcib3: Command Completed
pcib3: HotPlug interrupt: 0x30
pcib3: Command Completed
...

As a workaround disable HotPlug on the N1SDP as it's unlikely anyone
will depend on it.

Reviewed by: br
Fixes: 1f5c50a86173 ("pci_host_generic:Add pcib_request_feature on ACPI")
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D53134