Add CONFIG_BIOSEMU define to guard all the bios emulator code

Signed-off-by: Jason Jin <Jason.jin@freescale.com>

This patch fix the compile issue on the board that did not enable the bios emulator
diff --git a/drivers/bios_emulator/x86emu/ops2.c b/drivers/bios_emulator/x86emu/ops2.c
index 631a340..81c0d49 100644
--- a/drivers/bios_emulator/x86emu/ops2.c
+++ b/drivers/bios_emulator/x86emu/ops2.c
@@ -46,6 +46,8 @@
 
 #include "x86emu/x86emui.h"
 
+#if defined(CONFIG_BIOSEMU)
+
 /*----------------------------- Implementation ----------------------------*/
 
 /****************************************************************************
@@ -1768,3 +1770,5 @@
 /*  0xfe */ x86emuOp2_illegal_op,
 /*  0xff */ x86emuOp2_illegal_op,
 };
+
+#endif