build: add urandom-seed and urngd to default packages set

build: add urandom-seed and urngd to default packages set

urandom-seed content was split from base-files into separate package so
in order to preserve the current functionality and to provide some
fallback mechanism in case jent-rng initialization fails in urngd we
need to add it back.

urngd is OpenWrt's micro non-physical true random number generator based
on timing jitter.

Tested-by: Lucian Cristian <lucian.cristian@gmail.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
(cherry picked from commit f5387b754f98f85bf4a1c8c392a965bdbcb96db6)