Move DownloadProviderUi from core_minimal to core.mk

Move DownloadProviderUi from core_minimal to core.mk. This UI requires
DocumentsUi so it doesn't make sense to ship it on devices which are only
using core_minimal.

Change-Id: Id8a4f2a9835a05e9281596dbd5ca7b8e76062cd4
2 files changed