pci: move pci_ftpci100.h to include/faraday/ftpci100.h

Even though the header files is used only by the
pci_ftpci100 driver, it contains declaration for
a function which is used by external code.

Move the header file to a common location which
lets external code use it.

Compile tested only.

Cc: Macpaul Lin <macpaul@andestech.com>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>