drivers: entropy: nrf5: Fix dependency of the enabling Kconfig option

This driver makes use of the nRF RNG peripheral, so it can be used only
for SoCs that are equipped with one, and not all nRF SoCs are.
The option enabling the driver should then depend on `HAS_HW_NRF_RNG`,
which indicates the presence of this peripheral in a given SoC.

This patch removes also entries disabling this driver in default
configurations for nRF9160 SoC, as these were needed only because
of the invalid dependency of the ENTROPY_NRF5_RNG option.

A minor adjustment of Kconfig files of the nrf52_bsim board was
required as well, so that this board's configuration can properly
handle this corrected dependency.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>