There is no real reason for that pseudo-module to use the `gnrc_`
prefix. Neither does it need GNRC-components (except, but optionally, as
a network stack of course), nor is it implemented with in the GNRC
network stack.
This changes the prefixes of the symbols generated from USEMODULE and
USEPKG variables. The changes are as follow:
KCONFIG_MODULE_ => KCONFIG_USEMODULE_
KCONFIG_PKG_ => KCONFIG_USEPKG_
MODULE_ => USEMODULE_
PKG_ => USEPKG_