This allows to load private and public keys encoded in DER format.
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_
Expose 'CONFIG_CREDMAN_MAX_CREDENTIALS' to Kconfig
