PCI/VGA: Use pci_is_vga() to identify VGA devices

Use pci_is_vga() to identify VGA devices, so the arbiter will handle old
PCI_CLASS_NOT_DEFINED_VGA (0x0001) devices as well as the
PCI_CLASS_DISPLAY_VGA (0x0300) devices it previously handled.

Link: https://lore.kernel.org/r/20230830111532.444535-3-sui.jingfeng@linux.dev
Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
[bhelgaas: commit log, split functional change from optimization]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>

Author: Sui Jingfeng

drivers/pci/vgaarb.c

@@ -765,7 +765,7 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
 	u16 cmd;
 
 	/* Only deal with VGA class devices */
-	if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
+	if (!pci_is_vga(pdev))
 		return false;
 
 	/* Allocate structure */