x86 chipsets: Link non-code flow CHIPSET_BOOTBLOCK_INCLUDE files

Non-code flow assembly stubs do not have to be included in
bootblock.S, now that we have more freedom in bootblock linking.
Rather than bringing these stubs to the config system, just link them
in the bootblock.

Note that we cannot fully remove CHIPSET_BOOTBLOCK_INCLUDE at this
point, as some intel SOCs use this stub for code flow.

objdump -h build/cbfs/fallback/bootblock.debug on a few random boards
confirms that the appropriate sections are still included in the
final binary.

Change-Id: Id3f9ece14e399c1cc83090f407780c4a05a076f0
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: https://review.coreboot.org/11856
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
diff --git a/src/southbridge/sis/sis966/Makefile.inc b/src/southbridge/sis/sis966/Makefile.inc
index e703e1f..fa37762 100644
--- a/src/southbridge/sis/sis966/Makefile.inc
+++ b/src/southbridge/sis/sis966/Makefile.inc
@@ -16,5 +16,6 @@
 ramstage-$(CONFIG_USBDEBUG) += enable_usbdebug.c
 
 bootblock-y += romstrap.ld
+bootblock-y += romstrap.S
 
 endif