tests/tcg: unify ppc64 and ppc64le Makefiles

Make tests/tcg/ppc64le include tests/tcg/ppc64 instead of duplicating
the rules.  Because the ppc64le vpath includes tests/tcg/ppc64 but
not vice versa, the tests have to be moved from tests/tcg/ppc64le/
to tests/tcg/ppc64.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220929114231.583801-23-alex.bennee@linaro.org>