random: ctr_drbg: initialize on first run
random: ctr_drbg: initialize on first run

With f44b3dc4dfef4ba0adde064e910f35521f09232f statically initializing
the entropy_dev variable, `ctr_drbg_initialize` was not being run on
the first call to `z_impl_sys_csrand_get`. Use a dedicated static bool
to track whether the init needs to be run.

Signed-off-by: Jordan Yates <d74a90e280bbad1cc3646781a4e234b467b60fe1@data61.csiro.au>

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