rockchip: px30: use rockchip_stimer_init from spl_common.o for TPL

rockchip: px30: use rockchip_stimer_init from spl_common.o for TPL

Instead of redefining what is essentially the same code in
secure_timer_init, let's simply use rockchip_stimer_init from
spl_common.o instead.

This increases the size of the TPL by 16B, due to the added check of
STIMER already being enabled. Experimentally, STIMER is not already
enabled when in TPL.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>