armv8: layerscape: Enable routing SError exception

In case SError happens at EL2, if SCR_EL3[EA] is not routing it to
EL3, and SCR_EL3[RW] is set to aarch64, setting HCR_EL2[AMO] routes
the exception to EL2. Otherwise this exception is not taken.

Signed-off-by: York Sun <york.sun@nxp.com>