boards: opta: device tree cleanup

Some changes to cleanup and clarify some device tree nodes:

* removed wrong sdram2 definition
* added all internal flash slots accessible from M4
* added all internal flash slots accessible from M7
* removed CONFIG_UART_LINE_CTRL because not needed by USB CDC ACM

Signed-off-by: Federico Di Gregorio <fog@dndg.it>
3 files changed