lib/Makefile.inc: Add hexdump.c to postcar stage

hexdump() is not available in postcar stage.
Add hexdump() functionality to postcar stage.

BUG=NA
TEST=Booting Embedded Linux on Facebook FBG-1701

Change-Id: Ibdce911065c01b0a1aa81dc248557257d0e420b0
Signed-off-by: Frans Hendriks <fhendriks@eltan.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32908
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>

src/lib/Makefile.inc

@@ -166,6 +166,7 @@ postcar-y += imd.c
 postcar-y += romstage_handoff.c
 
 bootblock-y += hexdump.c
+postcar-y += hexdump.c
 ramstage-y += hexdump.c
 romstage-y += hexdump.c
 verstage-y += hexdump.c