modules: Kconfig: Unify the way of enabling instances in nrfx drivers

Use a consistent way of enabling particular instances of peripherals
in nrfx drivers through options defined in modules/Kconfig.nordic,
to make the usage of nrfx drivers in Zephyr, especially the ones for
which there are no Zephyr driver shims (yet), easier.

Jira: NCSDK-2744

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