Instead of trying to prevent pciconf from reconfiguring the firmware's
framebuffer, instead allow MD code to register callbacks. If a resource is
changed, the driver can unmap the old resource and remap the new. Do this
with simplefb so the console doesn't explode when the VGA device is
(potentially) reconfigured at boot.

Support early FB console attachment when booting with a devicetree
(non-ACPI mode). Inform the pciconf code about the framebuffer to
prevent pciconf from changing resources out from under us when framebuffer
memory is in VRAM.