armv8: fsl-layerscape: Add back L3 flushing for all exception levels

CCN-504 HPF registers were believed to be accessible only from EL3.
However, recent tests proved otherwise. Remove checking for exception
level to re-enable L3 cache flushing for all levels.

Signed-off-by: York Sun <york.sun@nxp.com>
Tested-by: Zhao Qiang <qiang.zhao@nxp.com>