flash/stm32l4x: add support of STM32WL5x dual core
according the RM0453, the second core have a different Flash CR and SR
registers for flash operations (called C2CR and C2SR).
so we need to a different flash_regs than older L4 devices.
@see stm32wl_cpu2_flash_regs
the C2CR register don't contain LOCK and OPTLOCK bits, and this explain
the addition of new register index called STM32_FLASH_CR_WLK_INDEX to
look-up the CR with lock, to be used in locking/unlocking the flash.
note: DBGMCU_IDCODE cannot be read using CPU1 (Cortex-M0+) at AP1,
to solve this read the UID64 (IEEE 64-bit unique device ID register)