kbuild: automatically include ECs

This change switches all ECs and the generic EC ACPI code
to be autoincluded by Makefile.inc, rather than having to be
mentioned explicitly in ec/Makefile.inc or in

This means, vendor and ec directories are now "drop
in", e.g. be placed in the coreboot directory hierarchy
without having to modify any higher level coreboot files.

The long term plan is to enable out of tree components to be
built with a given coreboot version (given that the API did not

Change-Id: I29d757d1f8c10a1d0167a76fd0d0f97bac576f6d
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/9798
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/src/ec/quanta/it8518/Makefile.inc b/src/ec/quanta/it8518/Makefile.inc
index ccceb6f..daf75ef 100644
--- a/src/ec/quanta/it8518/Makefile.inc
+++ b/src/ec/quanta/it8518/Makefile.inc
@@ -1,4 +1,8 @@
+ifeq ($(CONFIG_EC_QUANTA_IT8518),y)
 romstage-y += ec.c
 ramstage-y += ec.c
 smm-y += ec.c
 smm-y += ../../../lib/delay.c