tcg: Add insn_start_words to TCGContext

This will enable replacement of TARGET_INSN_START_WORDS in tcg.c.
Split out "tcg/insn-start-words.h" and use it in target/.

Reviewed-by: Anton Johansson <anjo@rev.ng>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/openrisc/sys_helper.c

@@ -26,7 +26,7 @@
 #ifndef CONFIG_USER_ONLY
 #include "hw/boards.h"
 #endif
-#include "tcg/tcg.h"
+#include "tcg/insn-start-words.h"
 
 #define TO_SPR(group, number) (((group) << 11) + (number))