Add device enumeration interface (v4)

Add an interface for enumerating PCI devices on
a system.

v3: switch to udev/sysfs for the enumeration
v4: fix warnings

Signed-off-by: Frank Min <frank.min@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>