Fix SepolicySplit soong variable

It should be "filtered" by "true" because all non-empty values become
true when using add_json_bool.

Test: m selinux_policy on sc-arc
Change-Id: I35d5881d83746230793cf8ced76885607e82334a
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 597ea78..c62086f 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -260,7 +260,7 @@
 
 $(call add_json_bool, SelinuxIgnoreNeverallows, $(SELINUX_IGNORE_NEVERALLOWS))
 
-$(call add_json_bool, SepolicySplit, $(PRODUCT_SEPOLICY_SPLIT))
+$(call add_json_bool, SepolicySplit, $(filter true,$(PRODUCT_SEPOLICY_SPLIT)))
 
 $(call json_end)