Add support for Sealevel 7xxxC serial cards.

This patch:
* Adds IDs to recognize 7xxxC cards from Sealevel Systems.
* Updates exar_pci_probe() to set nr_ports to last two bytes of primary
  dev ID for these cards.
Signed-off-by: Matthew Howell <matthew.howell@sealevel.com>
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2301191440010.22558@tstest-VirtualBoxSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>