doc: bindings: auxdisplay: add supported series

Add details on series supported by Noritake Itron driver.
Upon reading datasheets, series CU-TE, CU-Y, GU-3000, GU-7000 and
GU-D have commands matching the driver, whereas series CU-U, CU-TW,
and GU-800 use different command sets.

Signed-off-by: Eve Redero <eve.redero@gmail.com>