Update chromeec submodule to upstream master

Updating from commit id 860fe2962:
2018-12-29 05:45:29 -0800 - (mt_scp/ipi: Support host command.)

to commit id a1afae4e0:
2019-10-02 11:47:45 +0000 - (juniper: initial setup)

This brings in 1723 new commits.

Change-Id: Ieb4f00b21a4354bb634c3427c73260123b54ac2a
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35624
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

3rdparty/chromeec

@@ -1 +1 @@
-Subproject commit 860fe2962d40ee901369d1dc67f4aa7a7a42ba4d
+Subproject commit a1afae4e002a3eccd7835ac898259b0690e9e61a