arch/x86: Include timestamp.c in all stages

timestamp.c was not included in bootblock and postcar. This means that
these two stages would use the weak implementation in lib/timestamp.c
instead of the arch-specific implementation based on rdtsc.

This resulted in using timer_monotonic_get() which resets the
timestamps from 0. timer_monotonic_get() only provides per-stage
incrementing semantics on x86 because lapic implementation has
counting down values. A globally incrementing counter like rdtsc
provides the semantics like every other non-x86.

On the test configuration, the weak implementation of timestamp_get()
returned zero, resulting in wrong timestamps coming from the bootblock,
while romstage and ramstage used the arch implementation and returned
correct timestamps.

This is a great example of why weak functions are dangerous, and how
easy it is to miss subtle yet strong interactions between subsystems
and the coreboot buildsystem.

Change-Id: I656f9bd58a6fc179d9dbbc496c5b684ea9288eb5
Signed-off-by: Alexandru Gagniuc <alexandrux.gagniuc@intel.com>
Reviewed-on: https://review.coreboot.org/14860
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/arch/x86/Makefile.inc

@@ -97,6 +97,7 @@ ifeq ($(CONFIG_ARCH_BOOTBLOCK_X86_32)$(CONFIG_ARCH_BOOTBLOCK_X86_64),y)
 bootblock-y += boot.c
 bootblock-y += memcpy.c
 bootblock-y += memset.c
+bootblock-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
 bootblock-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
 
 bootblock-y += id.S
@@ -394,6 +395,7 @@ postcar-y += memset.c
 postcar-y += memcpy.c
 postcar-y += memmove.c
 postcar-y += memlayout.ld
+postcar-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
 postcar-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
 
 $(objcbfs)/postcar.debug: $$(postcar-objs)