Build from bl31 commit: 159eeff3185a92768427d31c2da7b7361dabd03e
update features:
Change ddr frequency with rk3399's private functions
The patch is the interim measures for changing ddr frequency.
Change-Id: I47dfb494677e0fe5321c9180e62d4b00fa57abfc
Signed-off-by: shengfei Xu <xsf@rock-chips.com>