[U-Boot] about rk3399 boot speed

Hi Philipp,

When I test on firefly-rk3399 with latest mainline U-Boot, it boots very very slow,

and it's due to the first time of cru driver bind(U-Boot proper) and the clk_set_defaults() cost about 5S.

Does puma board has the same problem?

Thanks,

- Kever