pci: drop unused Kconfig symbol

There's no other Kconfig symbol that depends on XEN_PCIDEV_FE_DEBUG.
Neither is there anything that uses CONFIG_XEN_PCIDEV_FE_DEBUG.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>