Add 'platform:' prefix to unqualified system server jars.

This allows Soong side changes to treat SystemServerJars as
android.ConfiguredJarList, same as boot jars.

Bug: 180105615, 155630745
Test: m && launch_cvd
Change-Id: I717d4351edcd82028ac19cb9265e18b98d11c661
diff --git a/core/dex_preopt.mk b/core/dex_preopt.mk
index dd31999..593ad66 100644
--- a/core/dex_preopt.mk
+++ b/core/dex_preopt.mk
@@ -62,7 +62,9 @@
 
 boot_zip := $(PRODUCT_OUT)/boot.zip
 bootclasspath_jars := $(DEXPREOPT_BOOTCLASSPATH_DEX_FILES)
-system_server_jars := $(foreach m,$(PRODUCT_SYSTEM_SERVER_JARS),$(PRODUCT_OUT)/system/framework/$(m).jar)
+system_server_jars := \
+  $(foreach m,$(PRODUCT_SYSTEM_SERVER_JARS),\
+    $(PRODUCT_OUT)/system/framework/$(call word-colon,2,$(m)).jar)
 
 $(boot_zip): PRIVATE_BOOTCLASSPATH_JARS := $(bootclasspath_jars)
 $(boot_zip): PRIVATE_SYSTEM_SERVER_JARS := $(system_server_jars)