rockchip: add driver for hardware RNG

rockchip: add driver for hardware RNG

Rockchip SoCs used to have a random number generator as part of their
crypto device, and support for it has to be added to the corresponding
driver.

Newer Rockchip SoCs like the RK3568 have an independent True Random
Number Generator device. Import pending patchset which adds a driver for
it, include it in Kconfig and enable it in the device tree.

Doing so significantly reduces the time needed to boot devices based on
those SoCs, from about 27 seconds until Ethernet is up and running to
less than 13 seconds with a minimal snapshot image.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>