lib: random: add get_crypto_bytes interface and use HWRNG if posssible
For crypto applications we need to use some thing else as PRNG.
So provide get_crypto_bytes() and use HWRNG as main source.
PRNG is allowed as fallback if user decided to configure it so.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>