boards: nordic: Add support for Thingy:53 as thingy53_nrf5340 board

Adding Thingy53 board with all required files including:
 - Kconfigs
 - dts
 - yamls
 - cmake
 - doc

Signed-off-by: Emil Obalski <emil.obalski@nordicsemi.no>
Signed-off-by: Georgios Titas <georgios.titas@nordicsemi.no>
18 files changed