Add framebuffer support to PicoLCD device with use of deferred-io.

Only changed areas of framebuffer get sent to device in order to
save USB bandwidth and especially resources on PicoLCD device or
allow higher refresh rate for a small area. Changed tiles are
determined while updating shadow framebuffer.
Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>