Move the vmap/vunmap blocks from the inner fb_dirty helpers into the
MIPI DBI update helpers. The function calls can result in waiting and/or
processing overhead. Reduce the penalties by executing the functions once
in the outer-most function of the pipe update.

This change also prepares for MIPI DBI for shadow-plane helpers. With
shadow-plane helpers, transfer source buffers are mapped into kernel
address space automatically.

v2:
	* keep each driver's existing buffer-mapping patter (Noralf)
	* zero-initialize iosys_map arrays (Noralf)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Noralf Trønnes <noralf@tronnes.org> # drm/tiny/mi0283qt
Link: https://patchwork.freedesktop.org/patch/msgid/20221202125644.7917-6-tzimmermann@suse.de