PCI: Move pci_rebar_size_to_bytes() and export it

PCI: Move pci_rebar_size_to_bytes() and export it

pci_rebar_size_to_bytes() is in drivers/pci/pci.h but would be useful for
endpoint drivers as well.

Move the function to rebar.c and export it.

In addition, convert the literal to where the number comes from
(PCI_REBAR_MIN_SIZE).

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patch.msgid.link/20251113180053.27944-4-ilpo.jarvinen@linux.intel.com