Testing turned out that the HWRNG quality varies greatly on RK3566,
even on supposedly identical boards and SoC revisions.
Hence enable the HWRNG driver only on RK3568 for now.
Allow users to simply tune sample_count and quality to allow easily
testing results on different boards and SoCs.
Link: https://patchwork.kernel.org/project/linux-arm-kernel/cover/cover.1720969799.git.daniel@makrotopia.org/
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
