PCI: pci-bridge-emul: Rename PCI_BRIDGE_EMUL_NO_PREFETCHABLE_BAR to PCI_BRIDGE_EMUL_NO_PREFMEM_FORWARD

This flag describe whether PCI bridge supports forwarding of prefetchable
memory requests in given range between primary and secondary buses. It does
not specify if bridge has support for prefetchable memory BAR (moreover
this pci-bridge-emul.c driver does not provide support for BARs).

So change name of this flag to be less misleading and add comment.

Link: https://lore.kernel.org/r/20220104153529.31647-4-pali@kernel.orgSigned-off-by: NPali Rohár <pali@kernel.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NRob Herring <robh@kernel.org>