bios_emulator: Add an option to enable debugging

At present there are DEBUG options spread around the place. If you enable
one and not another you can end up with an emulator that does not work,
since each file can have a different view of what the registers look like.
To fix this, create a global CONFIG_X86EMU_DEBUG option that keeps
everything consistent.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/bios_emulator/bios.c b/drivers/bios_emulator/bios.c
index bcc192f..152d70a 100644
--- a/drivers/bios_emulator/bios.c
+++ b/drivers/bios_emulator/bios.c
@@ -84,14 +84,14 @@
 			PM_outpb(0x3c2, PM_inpb(0x3cc) & (u8) ~ 0x02);
 			return;
 		}
-#ifdef  DEBUG
+#ifdef CONFIG_X86EMU_DEBUG
 		else {
 			printf("int42: unknown function AH=0x12, BL=0x32, AL=%#02x\n",
 			     M.x86.R_AL);
 		}
 #endif
 	}
-#ifdef  DEBUG
+#ifdef CONFIG_X86EMU_DEBUG
 	else {
 		printf("int42: unknown function AH=%#02x, AL=%#02x, BL=%#02x\n",
 		     M.x86.R_AH, M.x86.R_AL, M.x86.R_BL);