PCI: make SRIOV resources optional

From: Yinghai Lu <yinghai@kernel.org>

Allocate resources to SRIOV BARs only after all other required
resource-requests are satisfied. Dont retry if resource allocation for SRIOV
BARs fail.

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>