target/ppc: Disable goto_tb with architectural singlestep

The change to use translator_use_goto_tb went too far, as the
CF_SINGLE_STEP flag managed by the translator only handles
gdb single stepping and not the architectural single stepping
modeled in DisasContext.singlestep_enabled.

Fixes: 6e9cc373ec ("target/ppc: Use translator_use_goto_tb")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1795
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit 2e718e6657)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target/ppc/translate.c

@@ -4327,6 +4327,9 @@ static void pmu_count_insns(DisasContext *ctx)
 
 static inline bool use_goto_tb(DisasContext *ctx, target_ulong dest)
 {
+    if (unlikely(ctx->singlestep_enabled)) {
+        return false;
+    }
     return translator_use_goto_tb(&ctx->base, dest);
 }