x86/legacy: add missing config symbol

Signed-off-by: Jo-Philipp Wich <[email protected]>

target/linux/x86/legacy/config-default

@@ -149,6 +149,7 @@ CONFIG_ISO9660_FS=y
 # CONFIG_LCD_CLASS_DEVICE is not set
 CONFIG_LZO_COMPRESS=y
 CONFIG_LZO_DECOMPRESS=y
+CONFIG_M486=y
 # CONFIG_MDA_CONSOLE is not set
 CONFIG_MFD_CORE=y
 CONFIG_MFD_INTEL_LPSS=y