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/besys.c b/drivers/bios_emulator/besys.c
index 2a8e1a0..4c4bc8d 100644
--- a/drivers/bios_emulator/besys.c
+++ b/drivers/bios_emulator/besys.c
@@ -49,6 +49,7 @@
 
 #include "biosemui.h"
 
+#if defined(CONFIG_BIOSEMU)
 /*------------------------- Global Variables ------------------------------*/
 
 #ifndef __i386__
@@ -717,3 +718,4 @@
 #endif
 		LOG_outpd(port, val);
 }
+#endif