drm/hisilicon: Fixed pcie resource conflict between drm and firmware

use the drm_fb_helper_remove_conflicting_pci_framebuffer to remove
the framebuffer initialized by fireware/bootloader to avoid resource
conflict.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1582524112-5628-1-git-send-email-tiantao6@hisilicon.com