HID: picoLCD: rework hid-fbdev interaction

Split out all FB related data out of struct picolcd_data into a struct
picolcd_fb_data that is allocated with fb_info. This way fb_info may
cleanly outlive struct picolcd_data for as long as needed for its last
user to drop his reference.

Access to struct picolcd_data is now protected with struct
picolcd_fb_data's lock and tile  update reports are only generated
while picolcd_fbdata->picolcd is not NULL and is not marked as failed
(which indicates unplug in progress).

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>