Fix build by adding `cbmem.c` to `COLLECT_TIMESTAMPS`

A board without HAVE_ACPI_RESUME did not build with
COLLECT_TIMESTAMPS enabled as `cbmem.c` was not built.

Change-Id: I9c8b575d445ac566a2ec533d73080bcccc3dfbca
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/2549
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
diff --git a/src/lib/Makefile.inc b/src/lib/Makefile.inc
index 1c324fd..879ad7e 100644
--- a/src/lib/Makefile.inc
+++ b/src/lib/Makefile.inc
@@ -45,7 +45,7 @@
 romstage-$(CONFIG_CONSOLE_CBMEM) += cbmem_console.c
 romstage-$(CONFIG_CONSOLE_NE2K) += ne2k.c
 romstage-$(CONFIG_USBDEBUG) += usbdebug.c
-romstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
+romstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c cbmem.c
 romstage-y += compute_ip_checksum.c
 romstage-y += memmove.c