ANDROID: GKI: add CONFIG_BT to x86 gki_defconfig

It was enabled for arm64, but for some reason disabled for x86, which
led to lots of confusion when trying to do some build testing...

Bug: 157965270
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ic8e295c4d1f1cb368d386f2ba5ee1a5edbb83a96