pci: synquacer: Add SynQuacer ECAM based PCIe driver

Add ECAM based SynQuacer PCIe RC driver. This driver configures the
PCIe RC and filter out a ghost pcie config.

Since the Linux kernel expects "socionext,synquacer-pcie-ecam" device
is configured by firmware (EDK2), it doesn't re-configure in the kernel.
So as same as EDK2, U-Boot needs to configure it before boot the kernel.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>