HID: add experimental access to PicoLCD device's EEPROM and FLASH

The PicoLCD device has a small amount of EEPROM and also provides access
to its FLASH where firmware and splash image are saved.
In flasher mode FLASH access is the only active feature.

Give read/write access to both via debugfs files.

NOTE: EEPROM and FLASH access should be switched to better suited API,
      until then the will reside in debugfs

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