drivers/flash: STM32: use clk dt definitions in h7 flash driver
drivers/flash: STM32: use clk dt definitions in h7 flash driver

This commit replaces driver hard coded clk bus and enr definitions with
definitions from device tree.

Signed-off-by: Thomas Stranger <289fb7da2789c69f49f06a4b4e006530cf91f1de@outlook.com>

finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr