drivers: entropy: stm32: fix compile errors for STM32L4 series

The low level function names in the stm32l4xx low level driver are
different than all the other stm32's even though the functionality is the
same. This breaks the entropy module for these parts. This patch fixes the
build and has been tested on a custom stm32l4p5 board.

This STM32CubeL4 issue has been reported (ST Internal Reference: 207828).

Fixes: https://github.com/zephyrproject-rtos/zephyr/issues/88621



Signed-off-by: Matt Ihnen <matt.ihnen@gmail.com>