soc/intel/alderlake: Enable logging of wake sources for S0ix

This change adds elog.c and xhci.c to smm-y for alderlake platforms to
enable the logging of wake sources in eventlog for S0ix.

BUG=b:183684923
TEST=Verified on Brya that entry/exit for S0ix are logged in eventlogs.
295 | 2021-03-29 10:31:48 | S0ix Enter
296 | 2021-03-29 10:31:58 | S0ix Exit
297 | 2021-03-29 10:31:58 | Wake Source | RTC Alarm | 0

298 | 2021-03-29 10:32:30 | S0ix Enter
299 | 2021-03-29 10:32:55 | S0ix Exit
300 | 2021-03-29 10:32:55 | Wake Source | Power Button | 0
301 | 2021-03-29 10:32:55 | EC Event | Power Button

305 | 2021-03-29 10:43:13 | S0ix Enter
306 | 2021-03-29 10:43:14 | S0ix Exit
307 | 2021-03-29 10:43:14 | Wake Source | PME - XHCI | 0
308 | 2021-03-29 10:43:14 | Wake Source | PME - XHCI | 0
309 | 2021-03-29 10:43:14 | Wake Source | PME - XHCI (USB 2.0 port) | 8
310 | 2021-03-29 10:43:14 | Wake Source | GPE # | 109

Change-Id: Icc836caa797d3bc4e782c6a51492de23e7b49b71
Signed-off-by: Sugnan Prabhu S <sugnan.prabhu.s@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51839
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: EricR Lai <ericr_lai@compal.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/intel/alderlake/Makefile.inc b/src/soc/intel/alderlake/Makefile.inc
index 20e2fb3..5c1617b 100644
--- a/src/soc/intel/alderlake/Makefile.inc
+++ b/src/soc/intel/alderlake/Makefile.inc
@@ -45,11 +45,13 @@
 ramstage-y += systemagent.c
 ramstage-y += xhci.c
 
+smm-y += elog.c
 smm-y += gpio.c
 smm-y += p2sb.c
 smm-y += pmutil.c
 smm-y += smihandler.c
 smm-y += uart.c
+smm-y += xhci.c
 
 CPPFLAGS_common += -I$(src)/soc/intel/alderlake
 CPPFLAGS_common += -I$(src)/soc/intel/alderlake/include