target-i386: set G=1 in SMM big real mode selectors

Because the limit field's bits 31:20 is 1, G should be 1.
VMX actually enforces this, let's do it for completeness
in QEMU as well.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

target-i386/smm_helper.c

@@ -177,22 +177,22 @@ void do_smm_enter(X86CPU *cpu)
     cpu_x86_load_seg_cache(env, R_CS, (env->smbase >> 4) & 0xffff, env->smbase,
                            0xffffffff,
                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |
-                           DESC_A_MASK);
+                           DESC_G_MASK | DESC_A_MASK);
     cpu_x86_load_seg_cache(env, R_DS, 0, 0, 0xffffffff,
                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |
-                           DESC_A_MASK);
+                           DESC_G_MASK | DESC_A_MASK);
     cpu_x86_load_seg_cache(env, R_ES, 0, 0, 0xffffffff,
                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |
-                           DESC_A_MASK);
+                           DESC_G_MASK | DESC_A_MASK);
     cpu_x86_load_seg_cache(env, R_SS, 0, 0, 0xffffffff,
                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |
-                           DESC_A_MASK);
+                           DESC_G_MASK | DESC_A_MASK);
     cpu_x86_load_seg_cache(env, R_FS, 0, 0, 0xffffffff,
                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |
-                           DESC_A_MASK);
+                           DESC_G_MASK | DESC_A_MASK);
     cpu_x86_load_seg_cache(env, R_GS, 0, 0, 0xffffffff,
                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |
-                           DESC_A_MASK);
+                           DESC_G_MASK | DESC_A_MASK);
 }
 
 void helper_rsm(CPUX86State *env)