Don't panic if a resource is allocated twice.  Instead, print a warning and
fail the allocation request.  Allocations of "reserved" resources such as
PCI BARs already fail the request instead of panic'ing in this case.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272182 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f