tcg: Introduce tcg_use_softmmu

Begin disconnecting CONFIG_SOFTMMU from !CONFIG_USER_ONLY.
Introduce a variable which can be set at startup to select
one method or another for user-only.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/tcg/tcg.h

@@ -488,11 +488,9 @@ struct TCGContext {
     int nb_ops;
     TCGType addr_type;            /* TCG_TYPE_I32 or TCG_TYPE_I64 */
 
-#ifdef CONFIG_SOFTMMU
     int page_mask;
     uint8_t page_bits;
     uint8_t tlb_dyn_max_bits;
-#endif
     uint8_t insn_start_words;
     TCGBar guest_mo;
 
@@ -573,6 +571,12 @@ static inline bool temp_readonly(TCGTemp *ts)
     return ts->kind >= TEMP_FIXED;
 }
 
+#ifdef CONFIG_USER_ONLY
+extern bool tcg_use_softmmu;
+#else
+#define tcg_use_softmmu  true
+#endif
+
 extern __thread TCGContext *tcg_ctx;
 extern const void *tcg_code_gen_epilogue;
 extern uintptr_t tcg_splitwx_diff;