All the SoCs in 64-bit UniPhier SoC family support EL2.

Just hard-code MODE_EL2 instead of using el_implemented() helper.

Change-Id: I7ab48002c5205bc8c013e1b46313b57d6c431db0
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>