payloads/external: Add support for coreDOOM payload

coreDOOM is a port of DOOM to libpayload, based on the doomgeneric
source port. It renders the game to the coreboot linear framebuffer,
and loads WAD files from CBFS.

Tested with QEMU i440fx/q35 and a Dell Latitude E6400 using the
libgfxinit provided linear framebuffer.

Project page: https://github.com/nic3-14159/coreDOOM

Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Change-Id: Ice0403b003a4b2717afee585f28303c2f5abea5d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57222
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Martin L Roth <gaumless@tutanota.com>
diff --git a/payloads/Makefile.inc b/payloads/Makefile.inc
index a182bd6..0102ea3 100644
--- a/payloads/Makefile.inc
+++ b/payloads/Makefile.inc
@@ -29,6 +29,7 @@
 payloads/external/LinuxBoot \
 payloads/external/Yabits \
 payloads/external/skiboot \
+payloads/external/coreDOOM \
 
 force-payload: