tests/acceptance: Fix mismatch on cpu tagged tests

tests/acceptance: Fix mismatch on cpu tagged tests

There are test cases on machine_mips_malta.py and tcg_plugins.py files
where the cpu tag does not correspond to the value actually given to the QEMU
binary. This fixed those tests tags.

Reviewed-by: Cleber Rosa <crosa@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-Id: <20210430133414.39905-3-wainersm@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>