rockchip: rk3399: Support common spl_board_init

Support common spl_board_init by moving code from puma
board file into, common rk3399-board-spl.c.

Part of the code has sysreset-gpio, regulators_enable_boot_on
but right now only puma board is using this with relevant
config options rest remains common for all targets.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>