imx: imx8ulp_evk: Power down the domains may used in u-boot

Since ATF power domain will hold the enable counter for each power domain,
We need to power off them before entering kernel to avoid this
power domain can't be really powered off.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>