hyperv-fb: add pci stub

hyperv-fb: add pci stub

This patch adds a pci stub driver to hyper-fb.  The hyperv framebuffer
driver will bind to the pci device then, so linux kernel and userspace
know there is a proper kernel driver for the device active.  lspci shows
this for example:

[root@dhcp231 ~]# lspci -vs8
00:08.0 VGA compatible controller: Microsoft Corporation Hyper-V virtual
VGA (prog-if 00 [VGA controller])
        Flags: bus master, fast devsel, latency 0, IRQ 11
        Memory at f8000000 (32-bit, non-prefetchable) [size=64M]
        Expansion ROM at <unassigned> [disabled]
        Kernel driver in use: hyperv_fb

Another effect is that the xorg vesa driver will not attach to the
device and thus the Xorg server will automatically use the fbdev
driver instead.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>