cpu/stm32: STM32MP1 family has no flash
cpu/stm32: STM32MP1 family has no flash

Then CPU_FLASH_BASE cannot be defined as FLASH_BASE does not exist.

Signed-off-by: Gilles DOFFE <5872090fc9813271e12cf6b5c9dea3d3f95dd463@savoirfairelinux.com>

jasonatran/RIOT,authmillenon/RIOT,miri64/RIOT,miri64/RIOT,jasonatran/RIOT,jasonatran/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kYc0o/RIOT,authmillenon/RIOT,ant9000/RIOT,miri64/RIOT,kaspar030/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,ant9000/RIOT,kaspar030/RIOT,kYc0o/RIOT,authmillenon/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT,OlegHahm/RIOT,miri64/RIOT,authmillenon/RIOT,kYc0o/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,jasonatran/RIOT,kYc0o/RIOT,ant9000/RIOT,kaspar030/RIOT,kYc0o/RIOT,ant9000/RIOT,kaspar030/RIOT,miri64/RIOT