Added Xi8088 emulation. Patch from EluanCM.

src/xi8088.c

@@ -0,0 +1,36 @@
+#include "ibm.h"
+#include "io.h"
+#include "cpu.h"
+#include "keyboard_at.h"
+
+#include "xi8088.h"
+
+static uint8_t xi8088_turbo;
+
+uint8_t xi8088_turbo_get()
+{
+        return xi8088_turbo;
+}
+
+void xi8088_turbo_set(uint8_t value)
+{
+        xi8088_turbo = value;
+        if (!value)
+        {
+                pclog("Xi8088 turbo off\n");
+                int c = cpu;
+                cpu = 0;        /* 8088/4.77 */
+                cpu_set();
+                cpu = c;
+        }
+        else
+        {
+                pclog("Xi8088 turbo on\n");
+                cpu_set();
+        }
+}
+
+void xi8088_init()
+{
+        xi8088_turbo = 1;
+}