arch/x86: Avoid HAVE_SMI_HANDLER conditional with smm-class

Build of the entire smm-class is skipped if we have
HAVE_SMI_HANDLER=n.

Change-Id: I10b4300ddd18b1673c404b45fd9642488ab3186c
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34125
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Lance Zhao <lance.zhao@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/lenovo/l520/Makefile.inc b/src/mainboard/lenovo/l520/Makefile.inc
index 2aa7f0f..2ce116f 100644
--- a/src/mainboard/lenovo/l520/Makefile.inc
+++ b/src/mainboard/lenovo/l520/Makefile.inc
@@ -15,6 +15,6 @@
 
 romstage-y += romstage.c
 romstage-y += gpio.c
-smm-$(CONFIG_HAVE_SMI_HANDLER) += smihandler.c
+smm-y += smihandler.c
 
 ramstage-$(CONFIG_MAINBOARD_USE_LIBGFXINIT) += gma-mainboard.ads