trusted-firmware-a: re-enable generation of packages

There is no need to inherit nopackages. Even when the output binaries are being
consumed from deploy or sysroot, and the main binary package is not meant to be
installed in the rootfs, package generation is still useful for SDK use cases
and as a way to distribute sources (e.g. src.rpm/SRPM) in Distros.

Signed-off-by: Denys Dmytriyenko <denys@ti.com>
Reviewed-by: Diego Sueiro <diego.sueiro@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>