mini-emulator-mips: Add system.prop

Enable RIL by providing appropriate props:

rild.libpath=/system/lib/libreference-ril.so
rild.libargs=-d /dev/ttyS0

Change-Id: I574df52a7334158d6de9f036d36366d005a42e70
diff --git a/system.prop b/system.prop
new file mode 100644
index 0000000..137a0f9
--- /dev/null
+++ b/system.prop
@@ -0,0 +1,6 @@
+#
+# system.prop for generic sdk
+#
+
+rild.libpath=/system/lib/libreference-ril.so
+rild.libargs=-d /dev/ttyS0