nvmet: pci-epf: Always configure BAR0 as 64-bit

NVMe PCIe Transport Specification 1.1, section 2.1.10, claims that the
BAR0 type is Implementation Specific.

However, in NVMe 1.1, the type is required to be 64-bit.

Thus, to make our PCI EPF work on as many host systems as possible,
always configure the BAR0 type to be 64-bit.

In the rare case that the underlying PCI EPC does not support configuring
BAR0 as 64-bit, the call to pci_epc_set_bar() will fail, and we will
return a failure back to the user.

This should not be a problem, as most PCI EPCs support configuring a BAR
as 64-bit (and those EPCs with .only_64bit set to true in epc_features
only support configuring the BAR as 64-bit).

Tested-by: Damien Le Moal <dlemoal@kernel.org>
Fixes: 0faa0fe6 ("nvmet: New NVMe PCI endpoint function target driver")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>