tcg/ppc: ST_ST memory ordering is not provided with eieio

eieio does not provide ordering between stores to CI memory and stores
to cacheable memory so it can't be used as a general ST_ST barrier.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-of-by: Nicholas Piggin <npiggin@gmail.com>
Message-Id: <20220519135908.21282-3-npiggin@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

tcg/ppc/tcg-target.c.inc

@@ -1836,8 +1836,6 @@ static void tcg_out_mb(TCGContext *s, TCGArg a0)
     a0 &= TCG_MO_ALL;
     if (a0 == TCG_MO_LD_LD) {
         insn = LWSYNC;
-    } else if (a0 == TCG_MO_ST_ST) {
-        insn = EIEIO;
     }
     tcg_out32(s, insn);
 }