defconfig: move vendor defconfigs to vendor/ subdirectory

Move all defconfigs down one level to vendor/.  Create symlinks as
necessary for userspace components that are still hard-coded to the
older location.

Change-Id: I4628a10349139e760758071eca96c5020337aff9
Signed-off-by: Bryan Huntsman <bryanh@codeaurora.org>