hyperv-fb: kick off efifb early

Remove firmware framebuffer before initializing hyperv-fb.  Needed
on gen2 virtual machines.   Letting register_framebuffer handle the
switchover results in efifb still being active while hyperv graphics
are initialized, which in turn can make the linux kernel hang.

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