Add directory support to nsjail genrule

Trusty build requires a lot of files. Rather than globbing all such
files (more than 10,000 files), allowing bind-mounting directories makes
nsjail much more efficient. With this change, directories can be
directly bind-mounted with dirgroup modules and dir_srcs property of
genrule module.

dirgroup module and dir_srcs property will be allowed only to Trusty
builds.

Bug: 358302178
Test: m lk.elf.x86_64 lk.elf.arm64
Change-Id: I5938a57b7fb65f8fecce4a8f40aa4aedbf991135
diff --git a/android/Android.bp b/android/Android.bp
index 44cddcc..3b54326 100644
--- a/android/Android.bp
+++ b/android/Android.bp
@@ -52,6 +52,7 @@
         "defs.go",
         "depset_generic.go",
         "deptag.go",
+        "dirgroup.go",
         "early_module_context.go",
         "expand.go",
         "filegroup.go",