drm/hisilicon/hibmc: Implement hibmc_dumb_create() with generic helpers

The hibmc driver aligns scanlines to 16 bytes. By using the new pitch_align
argument of drm_gem_vram_fill_create_dumb(), convert hibmc over.

v2:
	* move changes to VRAM helpers into separate patch

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191203083819.6643-5-tzimmermann@suse.de