boards: arm: add initial support for Arduino UNO R4 Minima

Add support for the Arduino UNO R4 Minima.
This board is the newest version of Arduino that uses Renesas RA4M1 SoC.

This commit provides only limited support to simplify the initial
support patch.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@fujitsu.com>