vgaarb: Use dev_printk() when possible

Use dev_printk() when possible.  This makes messages more consistent with
other device-related messages and, in some cases, adds useful information.
This changes messages like this:

  vgaarb: failed to allocate pci device
  vgaarb: setting as boot device: PCI:0000:01:00.0
  vgaarb: device added: PCI:0000:01:00.0,decodes=io+mem,owns=io+mem,locks=none
  vgaarb: bridge control possible 0000:01:00.0

to this:

  pci 0000:01:00.0: vgaarb: failed to allocate VGA arbiter data
  pci 0000:01:00.0: vgaarb: setting as boot VGA device
  pci 0000:01:00.0: vgaarb: VGA device added: decodes=io+mem,owns=io+mem,locks=none
  pci 0000:01:00.0: vgaarb: bridge control possible

No functional change intended.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161117174758.16810.67625.stgit@bhelgaas-glaptop.roam.corp.google.com