tests/tcg/aarch64: Use stz2g in mte-7.c

We have many other instances of stg in the testsuite;
change these to provide an instance of stz2g.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230530191438.411344-19-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

tests/tcg/aarch64/mte-7.c

@@ -19,8 +19,7 @@ int main(int ac, char **av)
     p = (void *)((unsigned long)p | (1ul << 56));
 
     /* Store tag in sequential granules. */
-    asm("stg %0, [%0]" : : "r"(p + 0x0ff0));
-    asm("stg %0, [%0]" : : "r"(p + 0x1000));
+    asm("stz2g %0, [%0]" : : "r"(p + 0x0ff0));
 
     /*
      * Perform an unaligned store with tag 1 crossing the pages.