pci.4: Quote argument to -width for a list block

This fixes an mdoc warning and also properly indents this list. While
here, update the quoted argument to be the longest tag in the list.

Also while here, correct the description of pd_numa_domain. NUMA
domains are a property of the device, not of the driver.

Reviewed by: ziaee, imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D55770