The only managed mapping function currently is pcim_iomap() which doesn't
allow for mapping an area starting at a certain offset, which many drivers
want.

Add pcim_iomap_range() as an exported function.

Link: https://lore.kernel.org/r/20240613115032.29098-13-pstanner@redhat.comSigned-off-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>