modules: Move nrfx glue code to main Zephyr repository

Move nrfx glue code (nrfx integration files, related Kconfig entries,
and related part of CMakeLists.txt taken from the hal_nordic module)
to modules/hal_nordic/nrfx/ directory.
CMakeLists.txt located in modules/hal_nordic/ is now the main cmake
file for the hal_nordic module. It points back to cmake stuff related
to the nRF IEEE 802.15.4 driver that still remains in that module and
it adds the extracted nrfx part as a subdirectory.
Kconfig.nordic is renamed to Kconfig and moved to modules/hal_nordic/.
It sources nrfx related entries from that separate file.

Update also the manifest to point to accordingly modified hal_nordic
revision.

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