nb/intel/x4x: Expose x86_64 support

TESTED on foxconn g41m.

Change-Id: I2d5d5dfbd76a84aa400e44b4bc2ac4f3b5b6f739
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56022
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/x4x/Kconfig

@@ -12,6 +12,7 @@ config NORTHBRIDGE_SPECIFIC_OPTIONS
 	select INTEL_GMA_ACPI
 	select CACHE_MRC_SETTINGS
 	select BOOT_DEVICE_SPI_FLASH_NO_EARLY_WRITES
+	select HAVE_EXP_X86_64_SUPPORT
 
 config CBFS_SIZE
 	hex