tcg: Initialize cpu_env generically

This is identical for each target.  So, move the initialization to
common code.  Move the variable itself out of tcg_ctx and name it
cpu_env to minimize changes within targets.

This also means we can remove tcg_global_reg_new_{ptr,i32,i64},
since there are no longer global-register temps created by targets.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/ppc/translate.c

@@ -51,7 +51,6 @@
 /* Code translation helpers                                                  */
 
 /* global register indexes */
-static TCGv_env cpu_env;
 static char cpu_reg_names[10*3 + 22*4 /* GPR */
     + 10*4 + 22*5 /* SPE GPRh */
     + 10*4 + 22*5 /* FPR */
@@ -85,9 +84,6 @@ void ppc_translate_init(void)
     char* p;
     size_t cpu_reg_names_size;
 
-    cpu_env = tcg_global_reg_new_ptr(TCG_AREG0, "env");
-    tcg_ctx->tcg_env = cpu_env;
-
     p = cpu_reg_names;
     cpu_reg_names_size = sizeof(cpu_reg_names);