PCI: apple: Enable clock gating

These pokes are not required to make the PCIe port work, but it sounds
like this should save some power at least.

Link: https://lore.kernel.org/r/20211117141916.197192-1-marcan@marcan.st


Tested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>