meta-quanta: q71l: add compats

Adds the compatible layers for this machine configuration.

Tested: With a companion uboot configuration change patch was able to
build image.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ia517c46647249279a3cadd75e04eb1d8ff5df209
diff --git a/meta-quanta/meta-q71l/conf/layer.conf b/meta-quanta/meta-q71l/conf/layer.conf
index 80bae52..9e56160 100644
--- a/meta-quanta/meta-q71l/conf/layer.conf
+++ b/meta-quanta/meta-q71l/conf/layer.conf
@@ -7,3 +7,4 @@
 
 BBFILE_COLLECTIONS += "q71l"
 BBFILE_PATTERN_q71l = ""
+LAYERSERIES_COMPAT_q71l = "gatesgarth hardknott"