[avb]Add include dir to public config

Add avb directory explicitly as include directory in public config,
since it doesn't have an include directory.

Bug: 54894
Change-Id: I3a079755fa2918cb366729066c52f7ef0c562955
diff --git a/BUILD.gn b/BUILD.gn
index d9d7bb5..4d568d8 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -57,10 +57,14 @@
     "libavb_atx/avb_atx_validate.c",
     "libavb_atx/avb_atx_validate.h",
   ]
-  include_dirs = [ "." ]
   cflags_c = [
     "-DAVB_COMPILATION",
     "-Wno-implicit-int-conversion",
     "-Wno-shorten-64-to-32",
   ]
+  public_configs = [ ":public_include_dirs" ]
+}
+
+config("public_include_dirs") {
+  include_dirs = [ "." ]
 }