soc: arm: Remove CPU_HAS_NRF_IDAU's dependencies

CPU_HAS_NRF_IDAU is depending on SOC_SERIES_NRF91X and
SOC_NRF5340_CPUAPP.

This makes it more difficult to have an out-of-tree nrf SOC.

It is also an unnecessary dependency. There is no prompt for
CPU_HAS_NRF_IDAU, so it will not show up in menuconfig and it won't be
possible to enable it from a users Kconfig fragment.

The only way to enable it is to select it, and those that select this
option can themselves make sure that they only do so when appropriate.

Also, move NRF_SPU options out to SOC Kconfig files to also make
out-of-tree SoCs possible. With the added benefit of not polluting the
common soc/arm/Kconfig.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>