PCI/VGA: Select VGA devices earlier

Select VGA devices in vga_arb_device_init() and pci_notify() instead of in
vga_arbiter_add_pci_device().

This is a trivial optimization for adding devices.  It's a bigger
optimization for the removal case because pci_notify() won't call
vga_arbiter_del_pci_device() for non-VGA devices, so it won't have to
search the vga_list for them.

https://lore.kernel.org/r/20230830111532.444535-3-sui.jingfeng@linux.dev


Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
[bhelgaas: commit log, split from functional change]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>