feat(boards): Add BDN9 Rev2 board.

* Onboard stm32f072.
* 3 possible encoder positions.
* Underglow/per-key not yet support.

app/boards/arm/bdn9/bdn9_rev2_defconfig

@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: MIT
+
+CONFIG_SOC_SERIES_STM32F0X=y
+CONFIG_SOC_STM32F072XB=y
+# 72MHz system clock
+CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=72000000
+
+# Floating Point Options
+CONFIG_FPU=y
+
+# enable GPIO
+CONFIG_GPIO=y
+
+# Needed to reduce this to size that will fit on F072
+CONFIG_HEAP_MEM_POOL_SIZE=1024
+
+# clock configuration
+CONFIG_CLOCK_CONTROL=y
+
+# Clock configuration for Cube Clock control driver
+CONFIG_CLOCK_STM32_SYSCLK_SRC_PLL=y
+# use HSI as PLL input
+CONFIG_CLOCK_STM32_PLL_SRC_HSI=y
+# produce 72MHz clock at PLL output
+CONFIG_CLOCK_STM32_PLL_PREDIV=1
+CONFIG_CLOCK_STM32_PLL_MULTIPLIER=12
+CONFIG_CLOCK_STM32_AHB_PRESCALER=1
+CONFIG_CLOCK_STM32_APB1_PRESCALER=2
+CONFIG_CLOCK_STM32_APB2_PRESCALER=1