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/bios.c b/drivers/bios_emulator/bios.c
index ed5437e..7aa1bfb2e 100644
--- a/drivers/bios_emulator/bios.c
+++ b/drivers/bios_emulator/bios.c
@@ -43,6 +43,7 @@
 
 #include "biosemui.h"
 
+#if defined(CONFIG_BIOSEMU)
 /*----------------------------- Implementation ----------------------------*/
 
 /****************************************************************************
@@ -319,3 +320,4 @@
 	bios_intr_tab[0x6D] = int10;
 	X86EMU_setupIntrFuncs(bios_intr_tab);
 }
+#endif