Add missing /etc/pkg to BSD.root.dist

Approved by:	bapt
MFC after:	2 days
X-MFC-With:	r257145
Document that -a will output the device name when -u is not specified..
when -u is specified it is not...

update the docs to say that you can use full device names w/ -u, and
update the examples...

Submitted by:	#vbsdcon
MFC after:	3 days
Switch to using ofw_bus_search_compatible() table-driven compat lookup.
Add compat strings for Freescale Vybrid family SoCs.