drm/fb-helper: Perform damage handling in deferred-I/O helper

Call fb_dirty directly from drm_fb_helper_deferred_io() to avoid the
latency of running the damage worker.

The deferred-I/O helper drm_fb_helper_deferred_io() runs in a worker
thread at regular intervals as part of writing to mmaped framebuffer
memory. It used to schedule the fbdev damage worker to flush the
framebuffer. Changing this to flushing the framebuffer directly avoids
the latency introduced by the damage worker.

v2:
	* remove fb_dirty from defio in separate patch (Daniel)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20221115115819.23088-5-tzimmermann@suse.de