sys_rand32_get() crashes the application

[DurandA]

I updated the nRF Connect SDK to latest master. It currently uses Zephyr 7d20f2ebf2. Most of the time (~4 times out of 5), calling sys_rand32_get() crashes the firmware and the nRF9160 reboots.

As a temporary workaround, I enabled CONFIG_XOROSHIRO_RANDOM_GENERATOR.

[Martin Lesund]

Hi Durand,

sys_rand32_get() is a non-secure callable function,
which leads to some complication, and currently a risk of
hardfault (reset). Therefore use k_cycle_get32() instead