rng-tools: move to meta-oe

rng-tools: move to meta-oe

Nothing in oe-core depends on rng-tools anymore:
   e7e1bc43ca rng-tools: splitting the rng-tools systemd/sysvinit serivce as a package
so move it to meta-oe for people who still want to run rngd
as a service for some reason or for those who want to run rng-test.

Signed-off-by: Randy MacLeod <Randy.MacLeod@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>