ANDROID: cuttlefish: overlayfs: regression

commit 3f0d9e29
("ANDROID: Remove unused cuttlefish build infra") caused a
regression in adb-remount-test.sh by removing the
CONFIG_OVERLAY_FS configuration from the x86 configuration.

The gki/cuttlefish configuration for arm64 was not affected
by the regression as it is enabled there.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Test: adb-remount-test.sh
Bug: 138649540
Change-Id: I9e51475f1025f726e69c6f513099248bf452cc2d