create emulator_arm64 device for sdk_phone_arm64 to use

Changes are needed in generic_arm64 so that aosp_arm64 can be used to
distribute the GKI. These changes are incompatible with the emulator,
so modify the sdk_phone_arm64 product to use its own device.

Bug: 111538404
Change-Id: I57b77d7cbf503afffa8db45ad8b5ae635b4f4444
diff --git a/target/board/emulator_arm64/system_ext.prop b/target/board/emulator_arm64/system_ext.prop
new file mode 100644
index 0000000..2f8f803
--- /dev/null
+++ b/target/board/emulator_arm64/system_ext.prop
@@ -0,0 +1,5 @@
+#
+# system.prop for emulator arm64 sdk
+#
+
+rild.libpath=/vendor/lib64/libreference-ril.so