PCI: push deprecated pci_find_device() function to last user

The ISDN4Linux HiSax driver family contains the last remaining users
of the deprecated pci_find_device() function. This patch creates a
private copy of that function in HiSax, and removes the now unused
global function together with its controlling configuration option,
CONFIG_PCI_LEGACY.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>