arch: aarch64: do EL2 init in EL3 if necessary

If EL2 is implemented but we're skipping EL2, we should still
do EL2 init. Otherwise we end up with a bunch of things still
at their (unknown) reset values.

This in particular causes problems when different
cores have different virtual timer offsets.

Signed-off-by: James Harris <james.harris@intel.com>