drm/hisilicon/kirin: Use drm_gem_fb_create()

drm_fb_cma_create() is just a wrapper around drm_gem_fb_create() now,
so use the function directly.

Cc: Xinliang Liu <z.liuxinliang@hisilicon.com>
Cc: Rongrong Zou <zourongrong@gmail.com>
Cc: Xinwei Kong <kong.kongxinwei@hisilicon.com>
Cc: Chen Feng <puck.chen@hisilicon.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Xinliang Liu <z.liuxinliang@hisilicon.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/1506255985-61113-4-git-send-email-noralf@tronnes.org