PCI: rcar: Verify that mem_res is 64K-aligned

The lower 16 bits of the address, which is managed by mem_res, need to be
zero.  Check the address to verify this.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>