rockchip: theobroma-systems: ringneck: migrate to rockchip_early_misc_init_r

Only setup_boottargets differs from the original misc_init_r from
Rockchip mach code, so let's use rockchip_early_misc_init_r instead of
reimplementing the whole misc_init_r from Rockchip.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>