ARM: mvebu: coherency: fix registration of PCI bus notifier when !PCI

ARM: mvebu: coherency: fix registration of PCI bus notifier when !PCI

Commit bc06af10835e ("ARM: mvebu: use hardware I/O coherency also for
PCI devices") added a reference to the pci_bus_type variable, but this
variable is only available when CONFIG_PCI is enabled. Therefore,
there is now a build failure in !CONFIG_PCI situations.

This commit fixes that by enclosing the entire initcall into a
IS_ENABLED(CONFIG_PCI) condition.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1400598783-706-1-git-send-email-thomas.petazzoni@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>