target/s390x: Move DisasFields into DisasContext

target/s390x: Move DisasFields into DisasContext

I believe that the separate allocation of DisasFields from DisasContext
was meant to limit the places from which we could access fields.  But
that plan did not go unchanged, and since DisasContext contains a pointer
to fields, the substructure is accessible everywhere.

By allocating the substructure with DisasContext, we improve the locality
of the accesses by avoiding one level of pointer chasing.  In addition,
we avoid a dangling pointer to stack allocated memory, diagnosed by static
checkers.

Launchpad: https://bugs.launchpad.net/bugs/1661815
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200123232248.1800-5-richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>