rockchip: phycore_rk3288: remove phycore_init() function

The phycore_rk3288 board has a SPL size problem,
so remove phycore_init() function to stay within the limits.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Wadim Egorov <w.egorov@phytec.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>