arch/tile: sync up the defconfig files to the tip

This was inspired by mchehab@redhat.com's observation that we
didn't have EDAC configured on by default in both files.  In addition,
we were setting INITRAMFS_SOURCE to a non-empty string, which isn't
a very common default and required editing to do test builds.
Signed-off-by: NChris Metcalf <cmetcalf@tilera.com>