ARM: mvebu: Enable mvebu-soc-id on Kirkwood

Add the Kirkwood PCIe compatibility string to mvebu-soc-id, so that it
can get the SoC ID and revision from the PCIe endpoints.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>