rockchip/rk3399: do secure timer init in pmusram

we will use timer in pmusarm, when logic power rail shutdown,
the secure timer will gone, so need to initial it in pmusram.

Change-Id: I472e7eec3fc197f56223e6fff9167556c1c5e3bc
Signed-off-by: Lin Huang <hl@rock-chips.com>