PCI: xgene: Use PCI_VENDOR_ID_AMCC macro

Header file linux/pci_ids.h defines AMCC vendor id (0x10e8) macro named
PCI_VENDOR_ID_AMCC. So use this macro instead of driver custom macro.

Link: https://lore.kernel.org/r/20210927134356.11799-1-pali@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Krzysztof Wilczyński <kw@linux.com>