cxgb4: Warn if device doesn't have enough PCI bandwidth

Check if the device get enough bandwidth from the entire PCI chain to
satisfy its capabilities. This patch determines the PCIe device's
bandwidth capabilities by reading its PCIe Link Capabilities registers
and then call the pcie_get_minimum_link function to ensure that the
adapter is hooked into a slot which is capable of providing the
necessary bandwidth capabilities.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>