build system: Introduce manual file type

It's used for files with custom build rules, eg.
the objcopy stuff surrounding smm and sipi_vector.

Change-Id: Ie9ab4c9c6008ca42f82f768c5f33f90c7f5f4db5
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/9287
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

Makefile.inc

@@ -139,6 +139,11 @@ romstage-c-deps:=$$(OPTION_TABLE_H)
 verstage-c-deps:=$$(OPTION_TABLE_H)
 bootblock-c-deps:=$$(OPTION_TABLE_H)
 
+# Add handler to add no rules for manual files
+define generic-objs_manual_template_gen
+# do nothing
+endef
+
 #######################################################################
 # Add handler to compile ACPI's ASL
 define ramstage-objs_asl_template