fbdev: add remove_conflicting_pci_framebuffers()

fbdev: add remove_conflicting_pci_framebuffers()

Almost all PCI drivers using remove_conflicting_framebuffers() wrap it
with the same code.

v2: add kerneldoc for DRM helper
v3: propagate remove_conflicting_framebuffers() return value
  + move kerneldoc to where function is implemented

Signed-off-by: Michał Mirosław <[email protected]>
Acked-by: Bartlomiej Zolnierkiewicz <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/7db1c278276de420eb45a1b71d06b5eb6bbd49ef.1535810304.git.mirq-linux@rere.qmqm.pl