drivers: stm32: random: Initial STM32 random number generator driver

Add a STM32 LL based driver for the RNG processor. The RNG processor
is a random number generator, based on a continuous analog noise, that
provides a random 32-bit value to the host when read. The RNG passed
the FIPS PUB 140-2 (2001 October 10) tests with a success ratio of 99%.

Signed-off-by: Erwin Rol <erwin@erwinrol.com>