drm/pl111: Do not use deprecated drm_driver.{enable|disable)_vblank

Do not use deprecated drm_driver.{enable|disable)_vblank callbacks,
but use drm_simple_kms_helpe's pipe callbacks instead.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1518425574-32671-5-git-send-email-andr2000@gmail.com