Update SystemUI aconfig files to match new style

See go/sysui-aconfig-structure

Bug: 297872375
Test: build
Change-Id: Ide9ec71e572195d69f2e1995bd140b41f21e4041
diff --git a/packages/SystemUI/aconfig/Android.bp b/packages/SystemUI/aconfig/Android.bp
new file mode 100644
index 0000000..c1390b2
--- /dev/null
+++ b/packages/SystemUI/aconfig/Android.bp
@@ -0,0 +1,13 @@
+aconfig_declarations {
+    name: "com_android_systemui_flags",
+    package: "com.android.systemui",
+    srcs: [
+        "systemui.aconfig",
+        "accessibility.aconfig",
+    ],
+}
+
+java_aconfig_library {
+    name: "com_android_systemui_flags_lib",
+    aconfig_declarations: "com_android_systemui_flags",
+}