Create system.prop for GSI Pi

Properties for GSI Pi are not exactly the same as those for legacy GSI.
Create a new gsi_system.prop for GSI Pi to avoid reusing legacy
treble_system.prop used by legacy GSI (aosp_$arch_a(b) products).

Bug: 78605339
Test: build and observe the system/build.prop
Change-Id: I435e33558e244009af9a91a97580fd56591ff6f3
diff --git a/target/board/gsi_system.prop b/target/board/gsi_system.prop
new file mode 100644
index 0000000..4b54aaf
--- /dev/null
+++ b/target/board/gsi_system.prop
@@ -0,0 +1,5 @@
+# GSI always generate dex pre-opt in system image
+ro.cp_system_other_odex=0
+
+# GSI always disables adb authentication
+ro.adb.secure=0