PCI: uniphier: Set mode register to host mode

Set the mode register to host(RC) mode so that the host controller
mode is set-up consistently across SoCs.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
[lorenzo.pieralisi@arm.com: updated log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>