target/s390x: Simplify helper_lra

target/s390x: Simplify helper_lra

We currently call trigger_pgm_exception to set cs->exception_index
and env->int_pgm_code and then read the values back and then
reset cs->exception_index so that the exception is not delivered.

Instead, use the exception type that we already have directly
without ever triggering an exception that must be suppressed.

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20191001171614.8405-13-richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>