PCI: Add Silicom Denmark vendor ID

Update pci_ids.h with the vendor ID for Silicom Denmark. The define is
going to be referenced in driver(s) for FPGA accelerated smart NICs.

Link: https://lore.kernel.org/r/20210208150158.2877414-1-mhu@silicom.dk


Signed-off-by: Martin Hundebøll <mhu@silicom.dk>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tom Rix <trix@redhat.com>
Reviewed-by: Krzysztof Wilczyński <kw@linux.com>