PCI/P2PDMA: Remove reference to pci_p2pdma_map_sg()

PCI/P2PDMA: Remove reference to pci_p2pdma_map_sg()

commit 9a000a72af75886e5de13f4edef7f0d788622e7d upstream.

Update Documentation/driver-api/pci/p2pdma.rst doc and remove references to
obsolete p2pdma mapping functions.

Fixes: 0d06132fc84b ("PCI/P2PDMA: Remove pci_p2pdma_[un]map_sg()")
Link: https://lore.kernel.org/r/20231113180325.444692-1-tstruk@gmail.com
Signed-off-by: Tadeusz Struk <tstruk@gigaio.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>