PCI: Add pci_is_vga() helper

PCI: Add pci_is_vga() helper

The PCI Code and ID Assignment spec, r1.15, secs 1.4 and 1.1, define
VGA Base Class and Sub-Classes:

  03 00  PCI_CLASS_DISPLAY_VGA      VGA-compatible or 8514-compatible
  00 01  PCI_CLASS_NOT_DEFINED_VGA  VGA-compatible (before Class Code)

Add a pci_is_vga() helper to return true if a device is in either category.

These VGA devices use the hardwired legacy VGA resources
([mem 0xa0000-0xbffff], [io 0x3b0-0x3bb], [io 0x3c0-0x3df] and aliases), so
they require special handling if more than one is present in the system.

Link: https://lore.kernel.org/r/20230830111532.444535-2-sui.jingfeng@linux.dev
Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
[bhelgaas: commit log, drop !pdev test]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>