arm: Add support for MINI-M4 for STM32 Board

Add configuration, dts and documentation for the MINI-M4 for
STM32 board based on the STM32F415RG SoC.
See https://www.mikroe.com/mini-stm32f4

 for more details.

Signed-off-by: Kwon Tae-young <tykwon@m2i.co.kr>