backports: ifdef some pci functions

backports: ifdef some pci functions

struct msix_entry entry is defined only when CONFIG_PCI
is defined, resulting in warnings like:

backport-include/linux/pci.h:256:16: warning: 'struct msix_entry' declared inside parameter list [enabled by default]
backport-include/linux/pci.h:256:16: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]

wrap (also the mock function) with appropriate ifdef CONFIG_PCI.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>