PCI: designware-ep: Make dw_pcie_ep_set_bar() handle 64-bit BARs properly

Since a 64-bit BAR consists of a BAR pair, we need to write to both
BARs in the BAR pair to setup the BAR properly.

Link: https://lkml.kernel.org/r/20180328115018.31921-7-niklas.cassel@axis.com


Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
[lorenzo.pieralisi@arm.com: updated code according to review]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>