Expose kernel input headers for toolbox

Toolbox is moving to Android.bp, and its genrule needs access to these
kernel headers.

Test: mmma system/core/toolbox
Change-Id: I213a36e1f4bb5d4e3e3e105ed7ab01ec945014a2
diff --git a/libc/Android.bp b/libc/Android.bp
index 20648d0..cc83a66 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -2122,4 +2122,11 @@
     first_version: "9",
 }
 
-subdirs = ["*"]
+// Export these headers for toolbox to process
+filegroup {
+    name: "kernel_input_headers",
+    srcs: [
+        "kernel/uapi/linux/input.h",
+        "kernel/uapi/linux/input-event-codes.h",
+    ],
+}