modules: hal_nordic: add NRFX_GPPI config

The nrfx_gppi module is an abstraction over nrfx_ppi and nrfx_dppi
drivers. It now has a Kconfig option that is separate from nrfx_dppi and
by default it enables all PPI/DPPI instances, if available.

Signed-off-by: Rafał Kuźnia <rafal.kuznia@nordicsemi.no>