Some quirks search for a HyperTransport capability and use a hard-coded TTL
value of 48 to avoid an infinite loop.

Move the definition of PCI_FIND_CAP_TTL to pci.h and use it instead of the
hard-coded TTL values.

[bhelgaas: changelog]
Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>