boards: lilygo: add initial support for T-Watch S3

Most of the functionalities of the board are already supported in this
commit and they can easily be tested thought various Zephyr's samples and
tests.

What's still missing are:
- LoRA radio
- audio amplifier
- microphone
but these will be added in follow-up commits.

Signed-off-by: Valerio Setti <vsetti@baylibre.com>