ANDROID: build.config: Add vmlinux.symvers and modules.builtin to DIST_DIR

Copy vmlinux.symvers and modules.builtin to the DIST_DIR for mixed tree
builds. These files are used by the device kernel to modpost against the
GKI kernel.

These 3 new files add ~300 KB to the DIST_DIR

Bug: 178469391
Change-Id: Ic21a524aac05eafe18925982e860b0be9e6d8728
Signed-off-by: Elliot Berman <eberman@codeaurora.org>
Signed-off-by: Giuliano Procida <gprocida@google.com>
diff --git a/build.config.x86_64 b/build.config.x86_64
index b311320..ae4d41a 100644
--- a/build.config.x86_64
+++ b/build.config.x86_64
@@ -14,4 +14,7 @@
 arch/x86/boot/bzImage
 vmlinux
 System.map
+vmlinux.symvers
+modules.builtin
+modules.builtin.modinfo
 "