boards: opta: initial support for M7 core

Features enabled by this commit:

* M7 core available with or without the Arduino MCU-based bootloader by
  correctly initializing the external clock source.
* All LEDs, relays and the user button are mapped into the device tree
  (samples/common/blinky works out of the box).
* USB can be used in ACM mode (samples/subsys/usb/cdc_acm works without
  changes). The default Zephyr console is configured to use cdc_acm_uart0
  that in turn is assigned to the only USB port available.

Also enable USB stack to make sure that the console is available by default
and twister builds don't fail with missing device and added the default USB
vendor (0x35d1 Finder SpA) and product (0x0164) numbers to match the ones
used in the original product.

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